No abstract

FIVE PLATES (FIFTY-FIVE FIGURES) AUTHOR'S ABSTRACTOn the basis of experimental study and observations on the morphology of the legs of spiders, P. Friedrich described a cutting device within the trochanter which would sever that appendage from the body when the leg was stimulated by injury.A reinvestigation of the problem yielded entirely contrary results. Experiments calculated to induce spontaneous amputation through a n autoniatic reflex in the leg were negative on scorpions, harvestmen, and more than a dozen species of spiders. A detailed morphological study of the skeleton and musculature of the arachnid leg showed that no autotomizing device exists, either in the' skeleton or in the arrangement of muscles (as is usually supposed).

Until recently, it was universally accepted that erupted teeth (excepting those with persistent pulps) were incapable of further growth. I n 1927, however, Donaldson and French published a paper which may be summarized as follows:Casual inspection shows that the rows of molar teeth are longer and wider in older and larger albino rats than in younger and smaller individuals, in spite of the commonly accepted view that rooted teeth do not increase in diameter after eruption. The length of the rows of the three upper and lower molars, front to back, was measured on eightyseven cleaned skulls. For breadth the maximum width of each tooth was taken on sixty-four skulls, and the measurements for the three molars of each row were added together. Measurements from right and left sides were averaged. The average length of the tooth rows of the oldest group shows about 0.6 mm. increase over the youngest, associated with a total age range from 29 to 635 days. The average increase in the width of each tooth from the smallest to the largest group is about 0.2 mm. Both length and breadth show about 10 per cent differentials. For nineteen specimens studied, the main increase in the cross-section appears to be in the dentine rather than in the enamel, though the degree of wear may be a factor. The authors conclude that the molars continue to grow in both diameters long after eruption.One of us promptly pointed out the theoretical reasons against accepting this interpretation and offered various alternative interpretations of the data, one of which was 169 THE ANATOMICAL RECORD, TOL. 48, NO. 1