82 BULLETIN : MUSEUM OF COMPAEATIVE ZOOLOGY. 



are often, though not always, surrounded by a clear area, probably due 

 to shrinkage, and especially when they are small, the combination 

 looks very much like the nuclei with pale membranes and central 

 chromatic spots figured by Davidoff ('89, Taf. 5, Figs. 6, 7). But 

 the irregular occurrence of the clear area, the lack of a chromatic mem- 

 brane in the later stages, and the absence of transitions between them 

 and the test cell nuclei, show that they cannot be nuclei, and have 

 nothing to do with the formation of the test cells. 



b. Evidence for the Follicular Origin of the Test Cells. 



The first indication of the formation of the test cells is found in 

 the form and position of certain nuclei in the primitive follicle. 

 Whereas at first all the nuclei of the primitive follicle are oval, when 

 viewed in section, later one is occasionally encountered which js nearly 

 spherical and projects some distance into the cytoplasm of the ovum 

 (Plate 3, Fig. 13, cl. fol.). The space between the nucleus and the 

 egg cytoplasm I do not suppose to be occupied by the hyaline cytoplasm 

 of the forming test cell, as Floderus does in similar instances (p. 234), 

 but consider it as due primarily to shrinkage. In some instances I 

 believe that clear spaces thus formed were partially occupied by cytoplasm 

 during life; but in these cases I think that there was nothing but the 

 thinnest possible layer of cytoplasm between the follicle nucleus and 

 the egg, for in my most satisfactory preparations of this stage, where 

 the follicular cytoplasm is stained, none is usually encountered in this 

 place (Plate III., Figs. 24, 25). Here it is seen that the stained 

 cytoplasm of the follicle is not quite half as thick as the clear spaces 

 in Figure 13, and that even here shrinkage vacuoles are occasionally 

 present. They also show that in Distaplia no structureless membrane, 

 or chorion, has as yet been secreted on the inner surface of the follicle, 

 the line of demarcation between this surface and the ovum being 

 merely the cell membrane of the follicle cells. 



Figures 24 and 25 are from an ovum that is slightly older than that 

 shown in Figure 13, and in the height of test-cell production. About 

 half the follicle cells have rounded up, and either are on their way to 

 become test cells, or have actually become such. A majority of these 

 can be seen to be in cytoplasmic connection with the follicle. A 

 perfect series of the stages in the process can easily be made out, from 

 the enlarged follicle nucleus that is still in contact with the outer 

 membrane of that layer, through cases of progressive migration of the 

 nucleus and its accompanying cytoplasm into the ovum (Plate 3, 



