REGENERATION. 55 



VI. Regeneration. 



It has long been known that, in the marine Gymnolaemata, 

 the polypides in the older individuals of a colony are constantly 

 regenerated, the zooecium remaining unaffected by the processes of 

 degeneration. The remains of the degenerated polypide are found 

 as the so-called brown body suspended by strands of the funicular 

 tissue in the body-cavity. The regeneration of the polypide takes 

 place from the zooecial wall and, in the Chilostomata, in most cases 

 (according to Ostroumoff and Davenport, No. 11) on the operculum. 

 Harmer found recently that the first rudiment of the polypide is 

 paired and appears on the lateral margins of the operculum, the two 

 parts only uniting later to form an unpaired invagination. This 

 explains the abnormal cases in which, during regeneration, two 

 polypides are formed in one zooecium. By the invagination of the 

 two layers of the body-wall that now takes place, a new polypide 

 is produced in the way described above. It has long been known 

 that, during this process of regeneration, the wall of the stomach of 

 the new polypide comes into close contact with the brown body. 

 According to Haddon, the latter even passes through the wall into 

 the stomach of the newly-formed polypide, and Ostroumoff held 

 that during these processes entoderm-elements pass out of the brown 

 body into the wall of the stomach of the polypide, to take part in 

 the development of the latter (pp. 43 and 44). These statements, 

 however, have not been confirmed by Davenport's more recent 

 researches. According to Harmer, indeed, in Flustra, the brown 

 body is actually taken into the newly -formed alimentary canal, 

 although in Bugula this is not the case. 



We are still without any explanation of the significance of these 

 regenerative processes, which recall the regeneration of the head in 

 Phoronis, Pedicellina, and the Tubularia, and which may be com- 

 pared with similar processes in the Tunicata. We should, however, 

 mention Ostroumoff's view that, together with the brown body, 

 certain excreta are received into the intestine, which are afterwards 

 ejected through the anal aperture with the remains of the brown 

 body. Harmer's researches (No. 16) seem to some degree to support 

 this view. 



VII. General Considerations. 



Recent anatomical researches, especially those of Caldwell and 

 Cori, show that there is a great agreement between the structure 

 of Phoronis and that of the Ectoproctous Bryozoa. This similarity 



