128 BRITISH APHIDES. 



more easily described as gyratory, than like that ener- 

 getically displayed by sperm-cells in the higher animals. 

 These spermatozoids have a tendency also to gather 

 into knots. 



The process of separation of these elements from 

 their capsules is discussed by Balbiani. It does not 

 materially differ from that in other Insects. 



The before-noted capsules contain numerous cyst- 

 like bodies, composed of a definite membrane enclosing 

 a multitude of minute cells disposed at one end of 

 the cyst, and a bundle of filaments ranged parallel-wise 

 at the other. When the sperm-cells are mature the 

 cysts break up or burst, and the filamented cells dis- 

 entangle, and are then free to move down the vessels 

 into the suitable vesicles. 



As to the motion of these sperm-cells exterior to 

 their containing vessels and the spermotheca of the 

 female, I will quote the substance of Balbiani's words, 

 which have also reference to the nuclei and nucleoli 

 of these bodies. As I have not possessed the requisite 

 address to exhibit these mere points, which approach 

 the limits of microscopic definition, I may be permitted 

 to do so. 



" I will add that even when the sperm-cells have 

 attained their independent existence, they have never 

 presented to me (ne ni'ont jamais present e) any trace 

 of spontaneous movement ; but on subjecting them to 

 the action of a weak alkali, which notedly evokes the 

 movements of sperm-cells of other animals, it often 

 provoked feeble contractions ; but these disappear in a 

 short time. It is not, however, uncommon to see 

 the spontaneous movements of the spermatozoa 

 actively executed in the generative organs of the 

 female." 



Balbiani considers that there is a close analogy 

 between tin- sperm-capsule and the true ovum, and if 

 so, thai ilieiv should be analogically a nutritive mass 

 and a germinal centre in the former. The first is 

 thought by him to be represented by the nucleus 



