38 CONKLIN. [Vol. XIII. 



The Unsegmented Ovum (Fig. i). 



The spermatozoa meet the ova in the oviduct and are inclosed 

 with them in the egg capsules, but the maturation and fecun- 

 dation of the ova do not take place until after the capsules 

 have been laid. I have reserved for another paper the study 

 of the nuclear phenomena which underlie these processes. 



Two polar bodies are extruded : they are clear and vesicular, 

 and each contains a small nucleolus-like sphere of chromatin. 

 The chromatin in the first-formed polar body usually divides, 

 though the body itself frequently does not. Both polar bodies 

 remain attached exactly at the centre of the ectodermal area, 

 frequently until the ectoderm cells have extended more than 

 halfway around the egg. Figs. 49 and 50. In all these later 

 stages the chromatin is not surrounded, as in earlier stages, 

 by a clear vesicular layer of cytoplasm, but seems to have dis- 

 solved and spread throughout the whole body, so that it stains 

 quite uniformly. Sooner or later the polar bodies fall off and dis- 

 appear, and in sections of embryos of the stage shown in Fig. 93, 

 I have, in several cases, found them in the mesenteron, having 

 been drawn in with the nutrient fluid surrounding the embryos. 



The unsegmented ovum is nearly spherical in C. plana and 

 C. fornicata, though in the larger eggs of C. convexa and C. 

 adunca it is generally elongated in one diameter, so that when 

 seen from either pole the outline is elliptical.^ The protoplas- 

 mic portion in all of these species is small as compared with the 

 yolk, but much smaller relatively in the last two than in either 

 of the first two. There is no sharp boundary line between the 

 protoplasmic and deutoplasmic portions ; on the contrary, the 

 former sends out pseudopodia-like branches between the yolk 

 spheres, and the spheres themselves grow smaller and more 

 indistinct as one approaches the protoplasmic portion. Fig. i, 

 the earliest stage drawn, shows the male and female pronuclei 

 lying close together but still distinct. Each nucleus contains, 

 besides several bands or loops of chromatin, a homogeneously 

 staining nucleolus of considerable size, from which the bands 

 of chromatin seem to radiate. In the figure the female pro- 



^ McMurrich has pointed out that the eggs of Fulgur are elongated. 



