ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 179 



•cleavage, and the establishment of an inner layer, which in some cases, 

 as in Ammothea, forms a recognisable gastrula. The absence of a typical 

 gastrula in Ammothea leads us again to think of the lower Crustacea. 

 But even closer are the resemblances between the Protonymphon-larva 

 and the nauplius, which are discussed in detail. 



Allowing that the nauplius has many ccenogenetic characters, Meisen- 

 heimer cannot agree with Dohrn that the only relationship between 

 Crustaceans and Pantopods is in their common resemblance to an 

 " Ur-Form," far below the roots of both classes. " The larval develop- 

 ment of Pantopods points with great distinctness to a close relationship 

 with Crustaceans." 



Annulata. 



Regeneration in LimicolaB.* — Max Abel has reached the following 

 conclusions as to regenerative capacity in limicolous Chaetopods. The 

 regeneration of the anterior end of Tubifex usually occurs only after the 

 loss of fewer than 10-12 segments. The regenerated portion is divided 

 only into three segments. After amputation of numerous segments there 

 is in some rare cases development of regeneration-buds, but these do not 

 usually come to anything. 



In Nais, the regeneration of the anterior end is more frequent and 

 more rapid than in Tubifex, and occurs after the removal of many 

 segments as well as after the removal of a few. Six to eight segments 

 were often observed in the new growth. In both genera, the head-ends 

 do not regenerate a new tail-end unless they have at least 10-12 segments. 

 In both cases the regenerative capacity is markedly less towards the pos- 

 terior end. 



Portions of Tubifex from the anterior (genital) region frequently 

 form both anterior and posterior re-growths, while portions from the 

 other regions, usually re-grow only the posterior end, or less frequently 

 a normal anterior end. Portions of Nais from all regions of the body 

 except the hindmost region regenerate anterior and posterior ends 

 equally often. On the whole, the regeneration in Tubifex resembles 

 that in Lumbricidse, while Nais is more like Lumbriculus. The two 

 last-named forms have a greater regenerative power, and this may be 

 associated with their natural habit of asexual fission. 



The author then discusses the regeneration of the alimentary system 

 in particular. The lining of the new buccal cavity is ectodermic, but 

 the pharynx is endodermic, thus differing from what occurs in ontogeny. 

 The hind-gut is also regenerated from the ectoderm, but there are 

 frequent deviations from the ontogenetic form. 



Abel proceeds to describe the regeneration of the nervous system. 

 The cut-end of the old ventral cord" does not show any multiplication 

 of nerve-cells, and the frequent slight divarication of nerve-librils to 

 the body-epithelium is of subordinate importance in connection with 

 the regeneration. In the regeneration the nervous elements arise ex- 

 clusively from the ectoderm, which by proliferation forms an indifferent, 

 somewhat embryonic formative material, subsequently differentiated into 

 various structures, nervous and otherwise. In the regeneration, the 



* Zeitschr. wiss. Zool., lxxiii. (1902) pp. 1-74 (3 pis. and 2 figs.). 



N 2 



