38 THE TESTIS AND ITS SECKETION 



germinal spot or nucleus, situated about a third from the attached 

 extremity of the cell. In such of the spindle-shaped cells as are 

 quite full of secondary cells, this nucleus cannot be seen, so that 

 it probably disappears after the primary cells have become fully 

 developed, that is, have become full of young. In such of these 

 elongated cells, again, as are not quite developed, with cavities 

 not entirely occupied by their progeny, the nucleus may be oc- 

 casionally seen in various stages of developement, with a brood 

 of young cells surrounding it, and enclosed in a membrane car- 

 ried off' by them from the nucleus. (Pagurus.) 



These spindle-shaped primary cells of the lower part of the 

 seminal duct differ from the spherical primary cells of the upper 

 part of the same tube, principally in this, that whereas the latter 

 contain only a limited number of secondary cells, formed probably 

 by a single act of nuclear developement, the former are filled by 

 successive broods from the nucleus. 



In Hyas, when these spindle-shaped cells project from the ex- 

 ternal surface of the seminal duct, instead of into its cavity, 

 the secondary cells pass off by a narrow valvular orifice in its 

 attached extremity, and replaced by others from the nucleus. 

 The cell in this case has become a secreting follicle, with an 

 active germinal spot. 



The passage downwards of the secondary cells, both of the 

 superior spherical, and the lower spindle-shaped primary cells, is 

 retarded in the neighbourhood of the latter by long slips or 

 bands, which run up the cavity of the duct and terminate by free 

 edges ; the direction of these bands being opposed to the flow 

 of the seminal fluid downwards. 



These peculiar spindle-shaped cells or acini, although present 

 in all the orders, are most apparent in the Anomoura and cuirassed 

 Macroura. In the Triangulares and succeeding families of Brachy- 

 ura, also in lower families of Macroura^ from the Cryptobranchiate 

 genera and downwards, they are by no means so elongated, re- 

 sembling rather widened and contracted portions of the seminal 

 duct. The arrangement is similar in the lower orders as in 

 Stomapoda, Amphipoda, and Isopoda the Lcemodipoda being 

 apparently exceptions to the rule. Neither is this structure 

 found in Branckiopoda, Entornostraca, Siphonostoma, and Xip- 



