ZOOLOGY. 423 



part of the spindle remaining in the egg after the formation 

 of the second polar cell into a nucleus the female pronu- 

 cleus; (S) transportation of the female pronucleus towards 

 the centre of the egg; (9) entrance of one spermatozoon into 

 the egg; (10) conversion of the head of the spermatozoon 

 into a nucleus the male pronucleus; (11) appearance of ra- 

 dial striae round the male pronucleus, which gradually trav- 

 els towards the female pronucleus; (12) fusion of male and 

 female pronuclei to form the first segmentation nucleus. 



It may be remembered that Dr. E. L. Sturtevant contrib- 

 uted to the American Naturalist for August a note on the 

 development of unfertilized eggs in the body of the female 

 pickerel. In the October number of the same journal Dr. 

 W.K.Brooks gives the history of previously published cases 

 of a similar nature, with the authorities. Dr: Burnett saw in 

 eggs of the codfish before they were expelled from the ova- 

 ries, and therefore before impregnation, phenomena indicat- 

 ing that the segmentation of the yolk had already begun. 

 Agassiz declared that eggs in various early stages of devel- 

 opment may be found in the ovaries of the cod, whiting, and 

 hake. Bischoff states that a few unfertilized eggs of the 

 European frog were found to go through the early stages 

 of development, and this has been confirmed by another 

 French writer. Bischoff found eggs in various stages of 

 segmentation in the ovaries of a virgin sow, and Hensen ob- 

 served the same in the rabbit. Oellacher found that eggs 

 laid by virgin hens undergo segmentation and form a blasto- 

 derm while in the oviduct, and he regards this as a normal 

 process. Vogt says the unfertilized eggs of fflrola, a mol- 

 lusk, undergo segmentation, and Quatrefages records the 

 same occurrence in Unio. Dr. Brooks concludes that "the 

 egg has in itself the power to form a new individual, al- 

 though this power is never perfectly, and usually not at all, 

 shown until development is excited by the influence of the 

 spermatic filaments of the male." 



INVEETEBRATES. 

 Protozoa. 



Professor Leidy's recent investigations have led him to 

 suspect that the species of fresh-water Rhizopods are cos- 



