MIOROPYLE. 129 



known to all histologists ; the second is represented, 

 according to Balbiani, by the still smaller vesicle or 

 globule seen by him as furnished with a filament. 

 This he thinks he has established in the spermatozoid, 

 and it perhaps has been before indicated by Lavalette 

 Saint-George. Prof. Balbiani styles this last point " le 

 vesicule spermatogone," to suggest that it is analogous 

 to the corresponding element placed in the germina- 

 tive focus of the egg, that is to say, in the germinal 

 vesicle.* But there are good reasons for believing 

 that the sperm-capsule is the sole representative of the 

 ovum. The spermatic cells originate from cells indis- 

 tinguishable from the primitive ovum; so that the 

 fusion that takes place (at impregnation) is the fusion 

 of morphologically similar parts in the two sexes. 



Whatever function may be assigned to the nucleus 

 of the spermatozoon, it would appear that a single 

 head of the same penetrates into the vitelline sub- 

 stance, to seek the homologous body (female 'pro- 

 nucleus). These fuse together, and the result is 

 fertilisation, followed by segmentation of the yolk. 



The functions of the micropyle in Aphis perhaps are 

 of a double nature. Thus apparently it forms an orifice 

 for the entrance of nutritive matter, and also for the 

 spermatozoa. These functions may coexist. In Pliyl- 

 lajohis fagi the micropyle appears as a distinct lipped 

 orifice ; but in Lachnus longipes the appendage beyond 

 the summit of the ovum leads me to suppose that this 

 part really represents the polar cell or cells of the 

 ovum with its projecting spindle; rather than the 

 simple micropyle. 



If it be so, the knot of cells at the base of the 

 spindle might well represent the star-shaped body 

 seen by Fol. On the other hand, my figures are not 

 unlike those given by Prof. Huxley as probably con- 

 stituting micropyles.f 



* Balbiani, • Gen. de Aphides,' p. 82, et seq. 



f Balfour, ' Treat. Comp. Emb.,' pp. 20, 58, 69 ; also vide my figs. 6> 

 7, 8, 9, Plate H. \ also Huxley, 1. c, Plate 40. 



VOL. IV. 9 



