TESTIS IN DECAPODOUS CRUSTACEA. 433 



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 Brachyura, also in lower families of Macroura, from 

 the Cryptobranchiate genera and downwards, they are by no 

 means so elongated, resembling rather widened and contracted 

 portions of the seminal duct. The arrangement is similar in 

 the lower orders as in Stomapoda, Ampliipoda, and Isopoda 

 the Lcemodipoda being apparently exceptions to the rule. 

 Neither is this structure found in Branchiopoda, Entomostraca, 

 Siphonostoma, and Xipliosura, in which orders the structure 

 of the testis would require for elucidation a separate inquiry. 



The secondary cells, as has already been stated, continue 

 to be developed in their progress along the seminal tube. At 

 the spot where they are retarded by the folds at the necks of 

 the spindle-shaped cells, they increase much in size, from the 

 increased number and size of their contained cells. After this 

 no great change takes place, with the exception of a thinning 

 of the walls. In this state they pass along the narrow part 

 of the duct, or vas deferens, and are thrown during coitus into 

 the spermatheca of the female, there to undergo the essential 

 change which is to fit them for fertilisation of the ova. 



That this final change can only take place in the sperma- 

 theca of the female does not appear to be the case, for 

 precocious secondary cells may occasionally be found bursting 

 in the lower part of the seminal tube, and even as high up as 

 the spindle-shaped cells. The greater number, indeed, with a 

 few exceptions the whole of them, are introduced into the 

 female before bursting. 



2 F 



