1896.] Mr Harmer, On Cyclostomatous Polyzoa. 209 



polypides, whose rectum already contains the remains of Diatoms, 

 I have found evidence of the division of the nucleus of one of the 

 eggs, as well as some indication that the other eggs (if any) of the 

 same individual are degenerating. The development of an egg 

 takes place, however, in a very small proportion of the ovigerous 

 polypides, as is shown by the small number of ovicells and by the 

 fact that each ovicell contains but a single " embryophore V 



The next stage is the degeneration of the fertile polypide, as 

 in Lichenopora. Up to this time, there has been no external 

 difference between the young ovicell and an ordinary zocecium ; 

 but after this stage the ovicell becomes easily recognizable as such. 

 The punctate, calcareous film is the outer wall of a cavity con- 

 tinuous with the cavity of the fertile zooecium ; and this structure, 

 usually described as the " ovicell " or " ocecium," is thus merely a 

 dilated part of that zocecium. The young ovicell contains a small 

 brown body, the result of the degeneration of the fertile polypide, 

 with which are connected various structures, together composing 

 the embryophore. The latter differs considerably in detail from 

 that of either Crisia or Lichenopora, but parts corresponding with 

 the " tentacle-sheath " and the " follicle " of the former and with ' 

 the " suspensor " of the latter can be recognized. In a late stage 

 the embryophore contains a very large number of embryos in 

 various stages of development. Its proximal part is cylindrical 

 and lies in the body-cavity of that part of the fertile individual 

 which was developed before the more distal part of the same 

 individual took on the external characters of an ovicell. The more 

 distal part of the embryophore divides into several more or less 

 cylindrical lobes, which radiate out into the parts of the ovicell 

 lying between the oblique series of zocecia. I have convinced 

 myself that the " secondary embryos " arise by a process of em- 

 bryonic fission; but I propose to withhold the details of this 

 process for a later paper, in which I hope also to discuss certain 

 brown vesicles, occurring in the ovicells, polypide -buds, tentacles 

 and elsewhere, which retain their colour even in paraffin- sections, 

 and are hence an excessively conspicuous feature in preparations 

 of this species. 



The general results of this series of observations are as 

 follows : — 



(1) the normal occurrence of embryonic fission in Cyclo- 

 stomata is confirmed by the examination of a new case ; 



(2) the ovicell of Idmonea serpens is shown to be a modified 

 zocecium, and its early history is indicated ; 



(3) certain considerations suggest themselves with regard 

 to the classification of the Cyclostomata. 



1 See Quart. J. Micr. Set. xxxix. p. 94. 



