610 CLASS X. 



or not at all known. In certain of them the males occur only at 

 particular times of the year, and the females, like the leaf-lice, are 

 fruitful without copulation through several successive generations, 

 as in Daphnia and, according to JOLY, in Artemia. In others the 

 males may, on account of their minuteness, have eluded observation, 

 as in the parasitic genus Bopyrus, where they are surpassed in size 

 by the female about four times. Besides the unequal size, the 

 full-grown female in this and in other parasitic genera (Siphonos- 

 tomes) often present a very deviating form. The sexual difference 

 in the common form has not yet in the higher crustaceans been 

 sufficiently investigated in the different families. In the different 

 species of Limulus that difference is known pretty accurately. In 

 the long-tailed ten-footed crustaceans the males have larger claws 

 than the females, the last a broader abdomen than the first. 



As a rule the internal and external sexual organs are double. 

 In Argulus there is only one ovary with one oviduct opening be- 

 tween the two hindmost natatory feet, whilst however the external 

 organs in the male are double 1 '. The ovaries are ordinarily two 

 blind sacs, as for instance in the Isopods, elongate blind tubes. 

 Only seldom are they divided into branches, as in Chondracanthus 

 according to RATHKE, in Apus 2 and Limulus. They pass into two 

 oviducts, which open each separately. In Limulus the two vulvce are 

 near the first pair of abdominal feet, close to the basis at the dorsal 

 surface. In the ten-footed crustaceans these two external openings 

 are situated on the cephalothorax, between the feet of the third 

 pair, or on the base of these feet themselves. Only seldom, as in 

 Bopyrus, do the twa oviducts coalesce to form a single tube that 

 opens into a single vulva. Sometimes there are yet accessory 

 female organs, for the secretion of a covering of viscid fluid, either 

 to cover the eggs, or to take up the sperma, as the two large bursce 

 copulatrices in the short-tailed decapods 3 . The testes also have often 



1 Here at the first joint of the fourth pair of swimming-feet is seen a tubercle with 

 a hook directed backward. JURINE, Ann. du Museum, vn. pp. 448, 449, PL 26, figs. 

 i, 3, fig. 71. 



2 ZADDACH, De Apodis cancriformis Anatome et Historia evolutionis, Bonnse, 1841, 

 4to pp. 51, 52, Tab. i, fig. 14. 



3 See CARTJS Tdbul. anal. comp. illustr. Fasc. v. Tab. 3, fig. 7, /; comp. MILNE 

 EDWARDS Hist. not. dcs Crust, i. pp. 171 174 ; according to the observations of this 

 naturalist there is no room for doubt respecting the function of these parts (as poches 

 copulatrices}. 



