EMBRYONIC MISSION IN OYCLOSTOMATODS POLYZOA. 199 



On the Occurrence of Embryonic Fission in 

 Cyclostomatous Polyzoa. 



By 



Sidney F. Hai'iiier, M.A., B.Sc, 



Fellow of King's College, Cambridge, and Superintendent of the University 

 Museum of Zoology. 



With Plates XXII, XXIII & XXIV. 



The results of the present paper have formed the subject of 

 a preliminary communication made to the Cambridge Philo- 

 sophical Society (16). The case of embryonic fission which I 

 have now to describe in greater detail appears to me, on the 

 assumption that my explanation of the observed facts is the 

 correct one, to be without parallel in the animal kingdom. 



My observations refer entirely to the genus Crisia, and in 

 particular to a form common at Plymouth, which I have 

 described as a new species under the name C. ramosa (17). 

 The general results may be stated as follows : — 



(i) The ovicell, which is morphologically equivalent to a 

 zocecium, develops at the growing-point in the same way as an 

 ordinary zooecium. 



(ii) A polypide-bud is found in the young ovicell, consisting 

 of tentacle-sheath and a part which represents the alimentary 

 canal of a polypide. 



(iii) Small egg-cells are present in various parts of some of 

 the growing-points. One of these acquires a close relation to 

 the potential alimentary canal of the ovicell-polypide. 



(iv) This potential alimentary canal grows round the ovum, 

 losing its previous form, and becoming a compact multi- 



