IN Till-: DECAPOIMHS CIU'STACKA. ;j<) 



, in which orders the structure of the testis would require 

 tor 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 fertilization of the ova. 



That this final change can only take place in the spermatheca 

 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. 



After lying in the spermatheca for some time, the wall of the 

 secondary cell becomes so thin that it bursts, and allows the 

 young cells to escape. These tertiary cells contain, and are the 

 formative cells of the spermatozoa. In the higher Crustacea, 

 BrachyurO) they each contain one or more spermatozoa, in the 

 Macroura one only. The spermatozoal cells are nucleated when 

 they first burst from the secondary cells, and shortly the head of 

 the spermatozoa is found to correspond to the nucleus. 



The seminal fluid in all the species of Macroura is very pecu- 

 liar, the tertiary cells being in all cases armed with three long 

 slender seta?.* They are oblong, and dilated at the armed ex- 

 tremity. They are developed singly within their parent cells ; 

 sometimes, however, two may be observed in one cell. These 

 parent or secondary cells are oblong, and bulge slightly in the 

 middle. After they have remained for some time in the spindle- 

 shaped caeca (Galathea), the three seta? of the tertiary cell ex- 

 pand, and the cells begin their descent. In the progress down- 

 wards, the unarmed extremity acquires a small nucleated spot, 



* Von Siobold in Miiller's " J/v/> />..'' 1836. 



