RuPEUT JoNESj on B waived Entomostraca. 41 



concentrated; and the traces of the many ring-joints (or 

 " somites ") of which the Crustacean Animal is typically or 

 theoretically constructed are nearly lost to sight. Indeed, if 

 we trace the modifications of structure from one Crustacean 

 to another — from the many-segmented Brine-shrimp to the 

 more definitely jointed Woodlouse and Sandhopper, almost 

 equally ringed throughout the length of their bodies — and 

 through Squills and Shrimps with their carapace in front 

 and their armoured tail behind, and the Anomoura or short- 

 tailed members of the Lobster Tribe, until we get to the 

 Crabs, with scarcely any tail at all, we follow, as it were, the 

 footsteps of Nature in her advance from the lower and simpler 

 structures, with their many times repeated parts and organs, 

 to the higher, more concentrated, more complicated, more 

 specialised, and, in one sense, more perfect type of animal 

 structure. 



We see the carapace flat in the Crab ; in the Lobster it is 

 folded down on either side, and so we have it in many other 

 species ; but this folding is carried a step further in some 

 groups, the two halves being quite separate at the back, 

 along the central line that is Avell marked in the Lobster, 

 and becoming the two valves of a two-sided carapace, re- 

 sembling that of a common Bivalved Mollusc. 



This bivalved structure is not met with among the larger 

 Crustacea, but only in the smaller and frequently microscoj^jic 

 forms. These are members of the group known by the general 

 term "Water-fleas," or Entomostraca ("shelled insects"). 

 Some live in the sea, some in ponds and rivers. They exist 

 in countless numbers. Like the Sandhoppers, Shrimps, Lob- 

 sters, &c., they assist in the health-economy of the watery 

 world ; they are^cavengers, using up all dead matters. 



The Crustaceans have been termed " the Insects of the 

 Sea," and well they may, for they not only take the place of 

 Insects, Centipedes, and Spiders in the ocean, on every shore 

 and at nearly every depth, but they emulate the Insect-tribe 

 in the extremes of grace and ugliness. Though they can 

 scarcely be said to resemble the Insects in their flight, yet in 

 their flittings to and fro they are not unlike ; and in their 

 ceaseless, unwearying crawlings the likeness holds good ; — as 

 scavengers, too, they claim brotherhood with a world of 

 Beetles and other Insects. In this, however, as w^ell as in 

 the less amount of concentration of their organs, they differ 

 from Insects — namely, the changes which the latter undergo 

 are from one distinct stage to another, such as caterpillar, 

 chrysalis, butterfly ; but in the Crustacea we have successive 

 moul tings of the crust, with some alteration in the body. 



