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Cell lineages during development of leeches can be ascertained by injection of horseradish peroxidase as a tracer into identified cells at early stages of embryogenesis. The injected embryos continue their normal development, in the course of which horseradish peroxidase is passed on in catalytically active form to the descendants of the injected cell. The distribution of the tracer enzyme and hence of the progeny of the injected cell can then be observed at a later stage of development by staining the preparation for horseradish peroxidase.

Previously enigmatic, ovoid to sac‐like fossils of organic, acid resistant substance which are common components of leaf cuticle and megaspore assemblages in limnic and terrestrial palaeoen‐ vironments are identified as cocoons of clitellates. They have been recorded for a long time by palaeobotanists and palynologists, particularly in the Mesozoic, and have been variously interpreted as being of megaspore, seed, or algal origins, although convincing homologues were lacking. The fossils agree in basic wall construction with cocoons of clitellates, and particularly with certain members of the Hirudinea. A clitellate affinity is further supported by a possible segmentation, their consistently non‐marine occurrence, evidence for predation, and an example of amber‐like inclusion of alien structures in the cocoon wall which indicates the presence of secretion. As a consequence of the new interpretation, two taxa established under the botanical code of nomenclature for such fossils, namely Burejospermum crassitestum Krassilov and Dictyoth‐ ylakos pesslerae Horst, are transferred to the zoological kingdom and classified under Clitellata (phylum Annelida), along with two new taxa, D. spitsbergensis sp.n. andPilothylakospilosus gen. et sp.n. With the present interpretation a consistent Mesozoic record is documented for clitellates, a group of softbodied, basically freshwater and terrestrial animals of which there was until now nearly no fossil record.

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