32 BULLETIN OF THE 



A fourth diflference, which I do not remember to have seen mentioned, 

 concerns the position of the sexual glands. In Endoprocta they arise on 

 the polypide and are connected with the atrium by a special duct. In 

 Ectoprocta they arise on some part of the body wall. In all cases, how- 

 ever, they arise from the mesenchymatous tissue, or its equivalent, the 

 ccelomic epithelium. The exact position is not significant, for even 

 within the group of Phylactolsemata we find the testis arising sometimes 

 on the funiculus (Plumatella), sometimes on the body Avail (Cristatella), 

 and in neither case at the same place with the ova. 



On the other hand, the resemblances between Ectoprocta and Endo- 

 procta are striking : in both a curved alimentary tract, with tentacles 

 of similar histological structure ; in both, an atrium originating in the 

 same manner ; the central nervous system in both alike in position, 

 form, structure, and development ; in both the polypide originating in 

 comparable ways, involving the same problem of the relation of the germ 

 layers to the organs of the bud. Moreover, there must remain unmen- 

 tioned many minor resemblances which individually are not very signifi- 

 cant, but which, occurring together, furnish a most powerful argument to 

 tlie mind of one studying the animals themselves. 



. Hatschek's view seems to me, therefore, untenable, and it remains to 

 inquire whether the Bryozoa have been derived, accompanied by degen- 

 eration, from an Annelidan ancestry, through Gephyrean-like forms,^ or 

 whether they represent a persisting low type. As we have seen, the 

 first hypothesis must be relinquished, if it can be shown that the Endo- 

 procta are the more ancestral type. 



In any group of sessile, colonial animals, we should expect the more 

 ancestral type to retain more distinctly its individuality, to possess in a 

 more marked degree features belonging to a free, non-colonial life, and 

 in a less marked degree those belonging to a sessile, colonial one. Thus 

 in its development the group will lose certain characters and gain cer- 

 tain others.^ A well marked individuality accompanied by a simple 



1 As is well known, Hatschek ('83, p. 69) has long maintained that Phoronis and 

 the Sipunculaceae have not been derived from Annelids as the Echiurida have, but 

 from unsegmented ancestors ; and this view has become very widely accepted. 

 Ehlers, however, seems to adhere to the older view. Whatever the truth may be 

 in regard to this matter, the validity of my argument based on embryology and 

 comparative anatomy concerning the absence of close relationship between Pho- 

 ronis and Bryozoa is not affected. 



2 Lang ('88) has shown, by an instructive analysis, that in sessile animals loco- 

 motor and sense organs, the nervous system, and the musculature tend to degener- 

 ate, and that the tentacles and protective coverings become more important. 



