The nerve cord of nereid polychaetes consists of intersegmental ganglia linked by narrower connectives. Each ganglion gives rise to four pairs of peripheral nerves designated in their order of origin IV, I, II and III, but numbered I-IV in their segmental succession. Nerve I arises from the cord immediately behind the intersegmental septum, II (the parapodial nerve) and III leave the posterior end of the ganglion near the middle of the segment and IV originates from the anterior (preseptal) part of the succeeding ganglion at the posterior margin of the segment. Nerves I and IV cross the floor of the body wall transversely and terminate in the dorsal integument, II supplies the parapodium and III links ipsilaterally with homologous nerves of other segments through a lateral nerve which runs longitudinally in the ventral body wall adjacent to the bases of the parapodia. Nerves II are the largest, IV are next in size while I and III are very fine and visible only after staining. All the nerves are mixed and contain relatively few fibres. Each, on the afferent side, supplies a determinable region of the integument, I and IV between them drawing on integumentary receptors over the greater part of the ventral and the whole of the dorsal surface. Nerve II alone receives excitation from the parapodial integument and III is primarily proprioceptive, fibres entering the nerve from the surface of the dorsal and ventral longitudinal muscles. Sensory cells are most numerous in the parapodia, particularly in the cirri, and are present in large number in the ventral body wall. There are very few in the dorsal integument. Almost all are bipolar, usually single but occasionally grouped. Two morphological types of sensory cell are described. The internal (centrifugal) fibres of the sensory cells either run directly into the segmental nerves or, more frequently, discharge excitation into the nerve through tracts of a lattice-like subepithelial plexus made up of fibres of multipolar association cells. Excitation originating in scattered receptors thus appears to be canalized into the few fibres of the main nerves by way of the plexus. The internuncial systems of the cord through which the afferent (and efferent) fibres make their central connexion are of two kinds, (1) giant-fibres and (2) fine-fibres. The paired lateral and paramedial giant-fibres and the single median dorsal giant-fibre have a similar arrangement and distribution in Platynereis dumerilii and Nereis diversicolor to that described by Hamaker (1898) in Neanthes virens . The fine-fibre internuncial neurons are of two types: (1) with short, richly branching axons forming an extensive network in the dorsal neuropile and (2) with long axons, possessed of few collateral processes, forming six longitudinal tracts extending suprasegmentally as dorso-lateral, dorso-medial and ventral tracts disposed symmetrically about the midline. Within the ganglion internuncially transmitted excitation is carried, by virtue of the orientation of the fibres, ventrodorsally within the neuropile. Afferent fibres connect directly with one or other of the six fine-fibre longitudinal tracts. Proprioceptor fibres probably discharge into the dorso-medial region of the ganglion, exteroceptor fibres into its dorso-lateral area. In addition, afferent fibres, of unknown sensory connexion, enter the ventral fine-fibre tracts from nerves II and IV but not from I and III. Incoming afferent fibres, except perhaps in this latter instance where the ventral tract is adjacent to the lateral giant-fibre, appear never to excite giant-fibres directly. The latter are considered to be indirectly excited through the diffuse pathways of the neuropile. Motor axons arise, as do internuncial fibres, from cell bodies in the crescentic cell cortex of the ganglion. Every segmental nerve contains at least one motor axon which crosses the dorsal neuropile of the ganglion from a contralateral cell body, the axon giving off longitudinally alined collateral branches which connect directly with one or more of the dorsal fine-fibre tracts. Synapses between the dorsally crossing motor axons and the giant-fibres have not been observed, though a motor fibre of ventral emergence in nerve IV is synaptically connected with the lateral giant-fibre. The probable significance of these direct and indirect neuron interrelationships is discussed in relation to the responses of nereids and to previously described properties of the giant-fibres. Each segmental nerve contains, at its root, from one to four motor fibres. There is evidence of multiplication of the fibres at the periphery of the nerve, not by branching, but by the interpolation into the motor tracts of relay neurons. In one instance (the parapodial nerve distal to its ganglion) second-order motor neurons contribute additional fibres to the branches. These in turn connect with third-order neurons supplying the muscles. The terminal motor innervation has, however, been seen only in a few places. The peripheral connexions, both on their afferent and efferent sides, thus embody relay neurons, and it is considered that the arrangement may permit of the short-circuiting of excitation and of the possibility of extensive local control of movement. Evidence is presented to show that nerve IV may be mainly concerned with the innervation of the longitudinal muscles of the body wall through the contraction of which locomotory flexures are developed. Nerve II is responsible for the motor innervation of the parapodium. The occurrence of peripheral nervous connexions between the two nerves further suggests that the co-ordination of body flexures and parapodial movements may not be entirely dependent on central nervous linkages.

Comparison of the methods of adhesion and locomotion of the typical members of the four classes of the Eleutherozoa reveals a similarity of the adhesive mechanism in the Asteroidea, Echinoidea and Holothuroidea in that adhesion is due in part to suction and in part to the secretion of mucus. The ophiuroid, on the other hand, has tube feet which, because of their lack of a well-defined sucker, must adhere merely by their intrinsic stickiness. The ability to make use of suction results from the possession of a sucker so fashioned that the median part of the disk may be withdrawn from the surface of contact, with the resultant production of a vacuum. The sucker of the asteroid, echinoid or holothurian tube foot is well adapted for this purpose. An essential feature of such a disk is the presence of an arborescent system of connective tissue fibres extending from the basal plate to the outer limit of the ectoderm. By means of this system, the pull initiated by contraction of the longitudinal musculature of the podium is transmitted to the ectoderm of the sucking disk, the central part of which is thereby lifted up. Where suction plays no part in adhesion, as in the Ophiuroidea, the arborescent system of fibres is lacking.

In the year 1815, Tiedemann observed on the oral surface of the disk of the starfish Astropecten aurantiacus (L) a circumoral band of tissue continuous, in the mid-line of each arm, with a radial band. To these bands he ascribed a vascular function. Johannes Müller (1850), however, indicated that the radial and circular bands were more properly to be regarded as nerve cords, an observation which Owsjannikow (1871), Greeff (1871, 1872, a , 1872, b ), Hoffmann (1872), and Teuscher (1876) subsequently confirmed. Lange (1876), while not accepting the findings of previous authors as to the nervous nature of the circumoral and radial cords, discovered two ridges of tissue above each of the “V’’-shaped radial cords, one lying to the right and the other to the left of the mid-line. These are constituted by thickenings of the coelomic epithelium which lines the radial perihaemal canals, and were considered by Lange to represent nervous tissue. This opinion has been substantiated by Ludwig (1878), Hamann (1883, 1885), and Cuénot (1891) among others; but these and all recent investigators agree that the radial and circumoral cords must also be regarded as constituting part of the asteroid nervous system. Cuénot (1891) therefore distinguishes between the part of the nervous system derived from the ectoderm, such as the circumoral and radial cords, and the part—presumably of mesodermal origin—situated in the coelomic epithelium.

Summary (i) The general disposition of the sensory, association (internuncial) and motor elements of the starfish arm as revealed by intra‐vitam staining is described and figured (Fig. i), and (2) the nature of the nervous arcs responsible for reflex activities is discussed. (3) It is pointed out that the nature of the activities of an organ and the degree of integration of groups of organs are conditioned by the form and properties of the neurones and tracts through which they are innervated. (4) The pedicellariae, papulae and spines which are situated on, or are part of the dorsal body wall of a starfish are innervated through a plexus which has peripheral qualities. (5) There is little evidence of anatomical differentiation within the peripheral plexus except for the presence of groups of transversely running tracts which may correspond to the through‐conduction tracts (vide infra (8)). (6) The properties of the peripheral plexus are those of a nerve net as defined by Pantin (1935a, c) and the movements of the pedicellariae are analysed in relation to these properties. (7) The net shows evidence of differential capacity for facilitation in its various parts, in particular (8), there are transverse through‐conduction tracts in the plexus which, when coupled with the lateral motor systems of neurones (E of Fig. i) are the means of innervating the papulae and muscles of the body wall. (9) The movements and postures of the tube feet are described. (10) Together with the capacity of the feet to be co‐ordinated throughout the entire animal they demonstrate the central nervous properties of the circumoral ring and radial cords through which they are innervated. (11) These central nervous properties derive from the presence of special centres of co‐ordination, from a marked polarity of conduction, and from a certain configuration of the motor neurones within the central nervous system and the tube feet. (12) An account is given of the probable location and functions of the nerve centres and of the disposition of the nerve tracts within the central nervous system. (13) A brief reference is made to the effects of peripheral excitation on the pattern of coordinated movement of the podia.

Lignocelluloses represent a major source of renewable organic matter. Development of biological processing strategies normally must consider some form of pretreatment, hydrolysis of the polymers and bioutilization or bioconversion of these molecules to useful products. Bioprocessing technologies will usually involve low-moisture solidsubstrate fermentations. Landfill techniques are now widely practised and gas abstraction methods developed. Aerobic composting methods have gained increasing importance recently and set out to achieve brevity of process with low energy consumption, safe standard products for agricultural use and hygienic operation. ‘Open’ and 'closed’ composting systems are compared and evaluated. Single-cell protein has been produced from many lignocellulosic wastes and used for ruminant animal feeding. Current practices use pure-culture or mixed-culture bioprocesses. Mushroom cultivation is the most economically successful method for bioprocessing lignocelluloses and many commercial systems operate throughout the world.