24 SIDNEY F. HARMER. 



escape of the immature larvae. Wheu mature, the larvje force 

 their way one by one through the solid mass of protoplasm 

 into the tubular aperture, and so escape to the exterior. 



The tentacle-sheath is no longer easily distinguishable in 

 the mature ovicell. With the commencement of the vacuola- 

 tion of the follicle its distinctness vanishes, and it becomes 

 confounded with the vacuolated follicle. The relations shown 

 in figs. 9 and 17 probably indicate that the follicle ultimately 

 fills up the whole of the original tentacle-sheath, and that that 

 part of the ovicell which is not occupied by the protoplasmic 

 reticulum and its contents is the original body-cavity of the 

 ovicell. 



The ovicells which are at their period of greatest activity can 

 readily be recognised in the living condition by the pronounced 

 yellow colour of their contents. This is sufficiently distinct 

 to show clearly through the calcified wall of the ovicell. 

 Although the embryos and larvae are pale yellow, the colour 

 of the ovicell depends mainly on the pigment in the reticulum 

 which supports the embryos. In C. cornuta this is bright red- 

 orange in colour, while in C. ramosa the orange colour is not 

 quite so bright. 



The oldest larvee, which are almost ready to escape, lie each 

 enclosed in a distinct vacuole of the reticiilum, in close contact 

 with the thick mass of protoplasm which fills up the aperture 

 of the valve. 



The production of embryos continues up to a very late stage, 

 but embryos are always developed only from the budding mass 

 of embryonic cells (primary embryo). The budding organ has, 

 however, a somewhat different appearance in old ovicells 

 from that which it first had, both the secondary embryos and 

 their nuclei being markedly smaller than in the younger 

 ovicells. 



So far as my observations go, the whole of the budding 

 organ is ultimately used up in the production of embryos. In 

 ovicells which are nearly exhausted the embryos are few in 

 number, and the budding organ has been reduced to small 

 dimensions. Finally, the ovicell is found to consist merely of 



