CRUSTACEANS. 611 
the form of two blind sacs. Sometimes, as in the decapods, these 
have a more glandular aspect, and consist of an aggregate of many 
follicles. In the long-tailed ten-footed crustaceans the two testes 
form a single three-lobed body, though there are two vasa deferentia. 
These efferent tubes open in these crustaceans, as also in the short- 
tailed or crabs, at the base of the feet of the fifth pair. In these 
animals the external male organs of copulation have horny accessory 
organs attached to the first two abdominal rings which support the 
penis in copulation, and which as to their function may be compared 
with the little bone that occurs in this part in some mammals. 
The eggs of crustaceans after they have been laid often continue 
attached to different parts of the parent’s body, and there advance 
to further development. In the Onéscides, and many other crusta- 
ceans, the development takes place in a brooding eavity at the 
under surface of the anterior part of the body, where it is covered 
by a different number, commonly by five pairs, of ventral plates 
lying on one another like roof-tiles'. In Daphnia the eggs remain 
for some time in a cavity beneath the shell on the back; in Cyclops 
they are carried about in two bunches by the female at the base of 
the abdomen. The same is observed in many parasitic crustaceans. 
In others they are attached to the feet by an adhesive fluid hardened 
into threads; in the ten-footed crustaceans, to the feet of the abdo- 
men or of the so-called tail. Other crustaceans divest themselves 
of their eggs without bearing them about on their body, and attach 
them to other objects. Thus the female of Argulus foliaceus aftixes 
her numerous eggs (100—200) by means of a viscid covering to 
stones*. Cypris also lays her eggs upon different bodies under 
water, often in heaps of a hundred, which she covers with a green 
thready matter °. 
The egg of crustaceans, whilst still in the ovary, consists of the 
yolk, the germ vesicle, and the vitelline membrane. The Yolk is 
slightly fluid, and consists of shapeless fat-particles and cells, with 
only a small quantity of albuminous fluid. The germ-vesicle, 
which again includes different small vesicles (germ-spots), disappears 
after impregnation, as soon as the egg enters the oviduct. Here, on 
the other hand, it receives an external covering, a chorion, formed 
1 TREVIRANUS Verm. Schr. 1. Tab. Ix. figs. 51, 52. 
2 JURINE, |. 1. pp. 452, 453. 3 Srravus, Mém. du Mus. Vi. p. 54. 
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