200 SIDNEY F. HARMER. 



nucleated follicle surrounding the egg, which at first lies in an 

 exceutric cavity in the follicle. 



(v) The ovum segments^ and the blastomeres may, in early 

 stages, be completely separated from one another. The rela- 

 tions of the segmenting egg to its follicle are similar to those 

 described by Salensky (28) in Salpa (cf. Salensky's figs. 13, 

 13, on pi. x). 



(vi) The ovicell is meanwhile maturing, and by the end of 

 the segmentation of the ovum has been shifted to some dis- 

 tance from the growing-point by the superposition of new 

 zooecia above it. Its non-calcified aperture, which, at an earlier 

 stage, formed the wide end of a large funnel, has become 

 constricted, and has grown out into a long tubular orifice. 



(vii) At the end of segmentation, the embryo consists of a 

 small mass of undiff"erentiated cells, lying near the distal end 

 of the follicle, which has increased largely in size, and now 

 forms a spherical knob projecting freely into the interior of a 

 spacious tentacle-sheath. A complicated arrangement of cells 

 connected with the aperture has meanwhile been formed. 



(viii) The follicle becomes vacuolated, and is soon trans- 

 formed into a nucleated protoplasmic reticulum. The tentacle- 

 sheath loses its distinctness, 



(ix) The number of blastomeres increases, cell-limits being 

 indistinguishable at this, as at all other stages, excepting the 

 very earliest. 



(x) The embryo, having thus considerably increased in size, 

 although remaining a solid mass, without diff'erentiation of 

 organs, grows out into several finger-shaped processes, which 

 are generally directed towards the distal end of the ovicell. 



(xi) The finger-shaped processes are divided up by a series of 

 transverse constrictions into rounded masses of cells, each of 

 which becomes a complete larva. 



(xii) This process of embryo-formation continues during the 



whole functional period of the life of the ovicell, and is still 



actively proceeding at a stage when many of the embryos are 



mature, or nearly mature. The number of (secondary) embryos 



* The occurreuce of a process of fertilisation was not made out. 



