SEA-FISHERIES LABORATORY. 215 



about one-fourth the size of the ovary. Each vas deferens 

 courses posteriorly into the oval genital segment. It com- 

 municates with the sac of the spermatophore on the external 

 margin near the posterior end. A short cement gland 

 furnishes a duct which passes in at the anterior end of 

 the sac. The spermatophore, an oval body containing 

 the spermatozoa, is expelled from an opening near the 

 posterior angle of the segment. 



In LejJeophtheirus the fertilisation of the female is 

 accomplished soon after the " chalimus " stage is com- 

 pleted. The genital segment is then very small, about 

 one-fifth the length of that of a mature female. It is 

 grasped by the male on the dorsal aspect. The antennae 

 close round the junction of the genital segment with the 

 fourth thoracic, and the second maxillipedes seize the 

 segment immediately in front of its junction with the 

 abdomen. The animals remain in this condition for some 

 time, and can only be separated with difficulty. The 

 spermatophores are discharged in pairs. When they are 

 ready for discharging the male folds the whole of the 

 posterior portion of its body along the ventral surface of 

 the female. The openings of the spermatophore sacs are 

 thus brought in contact with the vulvae. The spermato- 

 phores are then discharged, and being in a viscid condi- 

 tion, at once stick to the female. One end of the cover- 

 ing, probably the last part that leaves the opening, is 

 drawn out into a fine thread, which helps to secure the 

 spermatophore. The spermatophores are not, apparently, 

 always fortunate in reaching the vulvae. It is by no 

 means uncommon to find them planted amongst the 

 appendages in little clusters like grapes. These have 

 been mistaken by some of the earlier Zoologists for the 

 eggs, when the true egg sacs were considered to be 

 antennules. 



