ON BUDDING IN POLYZOA. 547 



aware, it has been shown that representatives of the three 

 primary germinal layers enter into the bud, and there form 

 corresponding tissues, but, strangely enough, the Polyzoa form 

 an apparent exception to this rule, as the buds are said to arise 

 solely from the endocyst (Nitsche, &c.), or from the endosarc 

 (Joliet). Assuming the generally received opinion of the nature 

 of these tissues, in neither case would the bud have any hypo- 

 blast in its composition. It is inconceivable to me how a bud 

 could originate unless it possessed an offshoot from all the essen- 

 tial organs of its parent : that is to say, the bud should possess 

 a portion of the parental epiblast, mesoblast, and hypoblast ; 

 for how could either the epiblast or the mesoblast suddenly 

 depart from its ancestral traditions and take upon itself the 

 function of digestion? It is conceivable that, in process of 

 time, the method of gemmation should be considerably modi- 

 fied, but hardly that one of the most important of the three 

 primary embryonic tissues should not be represented at all. 

 Embryologists are fully conversant with variations in the deve- 

 lopment of organs, and with the masking of .the origin of certain 

 organs, as in the case of " precocious segregation,'^ but they 

 nevertheless have firm faith in the essential '^conservatism^' of 

 the layers themselves. 



The question now before us is : Are the three germinal 

 layers represented in the buds of Polyzoa ? The following are 

 my reasons for answering this in the affirmative, 



Nitsche and others, as we have noticed above, would derive 

 the whole of the bud from the endocyst — that is, from the 

 epiblast and peripheral mesoblast. Joli(^t, in combating this 

 view, points out that in Eucratea chelata and in all the 

 Cheilostomata which he has studied he has reason to believe 

 that the bud is really formed on some portion of the endosarc, 

 and not on the endocyst. In Hypophorella, Ehlers, the bnd 

 " is produced on the funiculus in the centre of the cell, as in 

 Eucratea. In many cases it is developed at the very base of the 

 zooecium, immediately over the communication plate or septum 

 and the orifices through which the connective threads pass, and 

 therefore probably in connexion with the endosarc. I [Ilincks] 



