ON THE ORIGIN OF THE EMBRYOS IN 



THE OVICELLS OF CYCLOSTOMATOUS 



POLYZOA. 



S. R HARMER, M.A. 



King's College. 



The species investigated belonged to the genus Crisia, in which, 

 as in other forms of Cyclostomata, the mature ovicells contain a large 

 number of embryos. These embryos are imbedded in the meshes 

 of a nucleated protoplasmic reticulum, which also contains a mass 

 of indifferent cells, produced into finger-shaped processes, the free 

 ends of which are from time to time constricted off as embryos. 

 The embryos have, at this stage, a structure identical with that of 

 the youngest embryos described by previous authors. After de- 

 veloping various organs, they escape as free larvse through the 

 tubular aperture of the ovicell. The budding organ from which 

 the embryos are formed makes its appearance at an early stage in 

 the development of the ovicell. Evidence was brought forward to 

 show that it must be regarded as an embryo, produced from an 

 ovum. The supposed ovum is found in very young ovicells, im- 

 bedded in a compact follicle, and appears to give rise, by a remark- 

 able process of development, to the budding organ above described. 

 The embryos are thus produced by the repeated fission of a primary 

 embryo developed in the ordinary way from an egg. 



