EMBRYONIC FISSION IN CYOLOSTOMATOaS POLYZOA. 41 



It hardly falls within the province of this paper to discuss 

 the details of the normal budding in Polyzoa. Both Braem 

 (5) and Davenport (8a) have shown that polypide-buds in 

 general are derived from a mass of "embryonic" tissue, handed 

 down from the beginning of the formation of the colony, 

 some part of this tissue being left over for the production of 

 fresh buds on each occasion when a polypide-bud is formed. 

 Braem's account of the formation of the statoblasts in Phylac- 

 tolsemata more nearly resembles the development of the 

 "secondary embryos" in Crisia than any other process as yet 

 described in Polyzoa. The funiculus is, indeed, not an em- 

 bryo ; but the young statoblasts are formed from it in much 

 the same way as that in which the larvae are developed from 

 the "primary embryo" in Crisia. The funiculus consists of 

 a core of ectoderm surrounded by a sheath of mesoderm (both 

 kinds of cells having an "embryonic" character). The stato- 

 blasts are formed by a process which is to all intents and 

 purposes a transverse segmentation of the funiculus. 



EXPLANATION OF PLATES I, II, & III, 



Illustrating Mr. Sidney P. Harmer's paper " On the Occur- 

 rence of Embryonic Fission in Cyclostomatous Polyzoa." 



PLATE I. 



EiG. 1.— CrisTa eburnea. Median longitudinal section through a young 

 ovicell, showing the egg, which is already partially surrounded by the polypide- 

 bud (Zeiss, DD). 



Fig. 2. — C. ramosa. Part of a similar section at a more advanced age, 

 showing the complete inclusion of the ovum (Zeiss, DD). 



Fis. 3. — C. ramosa. Similar section at an older stage. The polypide-bud 

 has become the "follicle." The tentacle-sheath and the aperture are well 

 developed. Ovicell at the "funnel-stage" (Zeiss, DD). 



VOL. VI. ' 4 



