64 BULLETIN OF THE 



Davenport, '90, Plate IX. Fig. 77, Plate XI. Fig. 98) and Paludicella 

 (Plate V. Figs. 50 and 45). 



As my purpose is not so much to present a complete organogeny of 

 Bryozoa as to show the method of origin of the bud and the fate of the 

 layers, I have had to desist from carrying on my studies further in the 

 organography, and have left many interesting and important questions 

 unsolved ; such, for instance, as the development and structure of avi- 

 cularia, the presence of an excretory system, and the degenerative pro- 

 cesses which occur with regularity in the polypides. 



3. Regeneration of the Poltpide. 



I have been led to study the regeneration of the polypide because 

 OstroumofF seems to believe that in regenerating buds the digestive epi- 

 thelium of the stomach is derived from an extraneous source, — the 

 brown body. Thus he says ('86', p. 340) the brown body appears as a 

 ccecal appendage of the young digestive tube. " C'est sur ce dernier 

 [tube digestif] qu'on trouve un groupe de cellules affectant la forme 

 d'un bonnet et se reunissant tres tot a Tangle proximal du rudiment 

 ectodermique. A mesure que les cellules du bonnet, ainsi que la masse 

 brune, sont employees a la formation de la portion moyenne du tube 

 digestif, ces dernieres se debarrasseut de leur contenu," etc. 



The external phenomena of regeneration are well known. In the 

 Membranipora stock, for instance, one sees polypides being produced at 

 the mai'gin, and one finds them older and older as one passes backwards, 

 until finally they are seen to be wholly degenerate, and to be replaced by 

 young polypides. Thus, in passing backward along a single row of indi- 

 viduals in a Membranipora stock about 18 mm. long, I have seen this 

 pi'ocess of regeneration recurring four times. In Alcyonidiun, too, one 

 finds an apparently regularly recuiTing degeneration and regeneration 

 of polypides. In the mat-like Cheilostomata the regenerating polypide 

 (Plate VIII. Fig. 71, pyd. rgn.) is always found at one place, — namel}^, 

 on the operculum, — that is, proximal of the opercular opening.^ • In 

 Flustrella it is found in a similar position on the dorsal body wall, proxi- 

 mal of the cuticularized introverted portion. My studies have been 

 chiefly made on the Cheilostomata. Figure 91 (Plate X.) represents an 

 early stage in the formation of a regenerating polypide. Here, as in the 

 marginal polypides, there is a typical invagination involving the two 



1 Haddon ('83, pp. 522, 523) has found the regenerating polypide arising from 

 the same place in Fhistra membranacea and in Eucratea, and Ostroumoff ('86», 

 p 339) in Cheilostomes in generaL 



