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 Lopyrus, 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!. ‘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? and Limulus. They pass into two 
oviducts, which open each separately. In Limulus the two vulve 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 two 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 burse 
copulatrices in the short-tailed decapods*. 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 Muséum, vu. pp. 448, 449, Pl. 26, figs. 
Py By 1 Oey 
2 Zapvacu, De Apodis cancriformis Anatome et Historia evolutionis, Bonne, 1841, 
4to pp. 51, 52, Tab. I, fig. 14. 
3 See Carus Tabul. anat. comp. illustr. Fasc. v. Tab. 3, fig. 7, £; comp. MILNE 
Epwarps Hist. nat. des Crust. I. pp. 17I—174; according to the observations of this 
naturalist there is no room for doubt respecting the function of these parts (as poches 
copulatrices). 
