ANIMAL BIOLOGY. [Part II. 



unite across the mid-line so as to envelope the posterior testes 

 and rosettes. Their lobes become much enlarged and grow out 

 backwards. Since they contain vast numbers of spermatozoa 

 in various stages of development, it is not surprising that these 

 large seminal reservoirs used to be regarded as the testes, and 

 that the true testes were overlooked. 



The true testes are largely made up of spherical sperm cells. 

 Of these cells the most superficial and furthest deyeloped 

 separate from the testes and pass into the seminal vesicles or 

 reservoirs which envelop them. These reservoirs are not 

 merely hollow sacs, but are divided by septa and vascular 

 trabeculse into a vast number of incomplete compartments. 

 Here the products of the testes are received and undergo further 

 development. 



The mode of development of the .spermatozoa is as follows : 

 The sperm cells, ere they leave the testis, undergo segmen- 

 tation, passing through stages in which there are 2, 4, 8, 16 

 nuclei, and so on. The nucleated masses thus formed tend to 

 stand out like buds from the cell that generates them, in the 

 midst of which there remains a passive unsegmented mass. 

 At this stage the whole is called a spermato-sphere, the bud-like 

 projections spermato-blasts, and the central bud-bearing mass the 

 blastophor. By this time the spermato-sphere has been detached 

 and is lodged in the seminal reservoir. As development here 

 proceeds each spermato-blast gives rise to a whip-like filament, 

 which continues to elongate, while the bud from which it pro- 

 ceeds becomes rod-like. Eventually each rod with its whip 

 separates off as a spermatozoon, the rod forming the head, and the 

 whip the tail. The blastophor probably atrophies. Although 

 there are differences in details, the principle involved in this 

 mode of development would seem to be typical. If, as is prob- 

 able, the sperm cell is to be regarded as equivalent to the germ 

 cell or ovarian ovum, then it must be noted that all the sperma- 

 tozoa derived from one such sperm cell are homologous with the 

 single ovum. 



The fully-developed spermatozoa are conveyed outwards by 



