PUTNAM ON PULVINARIA INNUMERABILIS. 329 



happens that but two of them appear in focus under the microscope at 

 the same time, and then they sometimes present a grotesque ovvl-lilie 

 appearance.) 



It seems probable that the vitelline membrane really extends around 

 and includes the vitelligenous cells, for, as the ovum approaciies its 

 final development the yolk globules extend gradually into the '•head" 

 forcing the vitelligenous cells into the upper p;irt (figs. 14-15). Tliis 

 continues until the vitelligenous cells finally disappear altogether,— 

 either being assimilated to the yolk globules or broken up and inter- 

 spersed between them. The yolk globules are now of very uniform size 

 and fill the entire ovum, including the " head'' (fig. 16). The epithelial 

 cells have entirely disappeared, and a firm but elastic chorian has been 

 formed around the ovum. The " head " is now but half the width and 

 less than a third the length of the ovicapsule, the dimensions being about 

 as follows : entire length of capsule 380 /^, greatest breadth 190// ; lengtli 

 of head, 90 //, breadth 100 /^ ; length of body 2D() n. The yolk globules are 

 about 15 fj. in diameter. 



"At the next stage in the development of the ovum an important change 

 takes place. The membrane of the ovicapsule gives way about the neck 

 and the ovum, in consequence of the elasticity of the chorion and 

 vitellus, assumes a regular oval form, the '-head'' becoming completely 

 collapsed, and its contents incorporated with that of the " body." After 

 the collaps^ing of the head the vitellus is seen to be still inclosed in a 

 vitelline membrane leaving a small space at each end between the 

 vitellus and chorion. If at this period there is a nucleus or germinal 

 vesicle I have not seen it, unless the gathering of granules at the two 

 ends be such. Previous to this stage the vitellus stains readily with 

 eosene, etc., now it does not, showing that the chorion has become com- 

 pleted and all openings closed. The ovum being now a fully developed 

 egg the membrane of the capsule gives way still more and allows the 

 egg to slip out into the general cavity of the ovary. 



FERTILIZATION OF TUB EGG. 



During the whole period of the development of the ova, large numbers 

 of the oval bodies (fig. 4) before mentioned {Pseudo-navicellcc.? ) are seen 

 all around and about them. At about the time of the collapse of the 

 *' head" of the ovicapsule a number of these bodies find their way inio 

 the ovum in some manner not fully accounted for, possibly by suction 

 caused by the collapse, in which case there must be an opening (or more 

 than one) in the chorion. I have frequently seen from five to twenty or 

 more of these bodies in the space at the anterior end between the vitellus 

 and chorion. They very soon appear to become disintegrated and the 

 inclosed granules set free. About the same time I have noticed a gath- 

 ering of granules at each end of the egg, that at tlie anterior end being 

 the larger; this granular substance spreads over the entire surface and 

 forms what I have supposed to be the blastoderm. This formation of the 

 blastoderm so promptly following the entrance of the oval bodies caused 

 me for a long time to believe that the latter were spermatophores, but as I 



