MUSEUM OF COMPARATIVE ZOOLOGY. 123 



of the individual of Alcyonella, for all of it, according to Braera, is de- 

 rived from the neck of ite own polypide. This last method of origin 

 of the body-wall I believe to be also present in Cristatella, as well as in 

 Alcyonella, as I shall have occasion to show later (page 144). 



In Paludicella, according to both AUman ('56, pp. 35, 36) and Korot- 

 nefF ('75, p. 369), the formation of the body-wall of the new individual 

 is begun before the appearance of the polypide. In Cheilostomata, as 

 both Nitsche ('71, p. 22) and Vigelius ('84, p. 75) have shown, and in 

 Ctenostomata, as demonstrated by Ehlers ('76, pp. 91, 92), the " zooe- 

 cium " arises before the polypide takes on its deBnite form. 



3. Origin of the Layers. — Although later researches have only con- 

 firaied the conclusion arrived at long ago, that in Tunicates cells from 

 all three germinal layers of the parent pass over into the bud, the 

 facts in Bryozoa have seemed not to favor the view of the fundamen- 

 tal nature of this process. To be sure, Hatschek ('77, pp. 517-524) 

 believed that he had found evidence of a condition in the budding 

 of Pedicelliua exactly comparable with that in the budding of Tuni- 

 cates ; but the more recent studies of Harmer ('86, p. 255) and Seeliger 

 ('89) have failed to confirm his results, if they have not satisfactorily 

 explained the source of his error. 



What is the relation of the condition I have described in Cristatella 

 to the question of the transmission of a part of each germinal layer to 

 the bud, and in how far do the conditions here agree with our present 

 knowledge of the budding process in other groups of Bryozoa] Al- 

 though my results accord with Hatschek's in this, that the youngest 

 and next older buds are intimately related, that the corresponding 

 layers in each are derived from the same cell layers, and that the inner 

 layer of the bud is not derived directly from the overlying ectoderm, 

 they do not strengthen the idea of the fundamental importance of his 

 doctrine, "Die Schichten der jiingeren Knospe stammen von denen der 

 nachst alteren direct ab." Moreover, they afford no evidence of the 

 accuracy of his conclusion, that the inner layer of the bud is com- 

 posed of entoderm ; indeed, since this inner layer does not give rise to 

 the alimentary tract alone, as he supposed, but to the nervous system 

 jilso, the facts in Cristatella tend to weaken his hypothesis. In order to 

 determine finally just what the origin of the stolon from which the 

 inner layer arises is, it will be necessary to study the origin of tlie first- 

 formed polypides. This I have not yet been able to do. Our present 

 knowledge on the subject is still in an unsatisfactory state. 



Allman ('56, pp. 33, 34) has described and figured some stages in the 



