CRUSTACEA. 347 



The more minute Crustacea, or Entomostraca, as they are 

 called by zoologists, in their mode of reproduction, offer several 

 remarkable variations from what has been described above ; and a 

 brief account of their most interesting peculiarities is therefore 

 still wanting to complete this part of our subject. These little 

 creatures, in fact, seem to form a transition between the class we 

 are now considering and the Epizoa, which many of them re- 

 semble so nearly that they are still confounded together by many 

 authors. The female Entomostraca frequently carry their ova in 

 two transparent sacculi attached to the hinder part of the body, 

 and it is in these egg-bags that the oviducts terminate ; so that 

 the ova, as they are formed, are expelled into the singular re- 

 ceptacles thus provided. Without such a provision, indeed, it 

 would be difficult to conceive how the ova could possibly remain 

 attached to the parent, as they far surpass in their aggregate bulk 

 the size of her entire body, and could not, therefore, by any con- 

 trivance be developed internally without bursting the crustaceous 

 covering that invests the mother. J urine,* Ramdohr,*)" and other 

 authors, have carefully watched the generative process in several 

 genera, and brought to light many important and curious facts 

 connected therewith. In Cyclops, a species to be met with in 

 every ditch, the impregnation of the ova is undoubtedly effected 

 in the body of the parent, and the eggs when formed are expelled 

 into two oval sacs placed on each side of the tail, which Jurine calls 

 external ovaries. The number of eggs contained in these sacs 

 gradually increases, and they exhibit a brown or deep red colour, 

 until a short period before the growth of the embryo is completed, 

 when they become more transparent. In about ten days the eggs 

 are hatched and the young escape ; but such is the prodigious 

 fertility of these little beings, that a single female will, in the 

 course of three months, produce ten successive families, each con- 

 sisting of from thirty to forty young ones. 



In the genus Apus, another plan is resorted to for the protec- 

 tion of the ova: the eleventh pair of legs, called by Schcefer\. 

 " womb-legs," have their first joints expanded into two circular 

 valves, which shut together like a bivalve shell, and thus form a 

 receptacle in which the eggs are contained until they arrive at 

 maturity. 



* Histoire des Monocles. 1 vol. 4to. Gen. 1820. 



f- Materiaux pour 1'Histoire de quelques Monocles A Demands. 4to. 1805, 



$ Apus pisciformis, insecti aquatic! species noviter delectae. 4to. Ratisbonne, 1757. 



