1 54 AMPHIPODS. 



ceding chapter. Its carapace covers only the anterior half of the thorax ; the hinder 

 portion being formed of rings like those of the abdomen. It is provided with enormous 

 claws, terminating in a sharp hook ; the last joint furnished with six sharp projecting 

 spines, and the preceding joint with three, and so hollowed as to render this claw a 

 most efficient instrument of prehension. The other foot-jaws, and the three anterior 

 pairs of thoracic members, share in this conformation, and serve to hold the prey 

 against the mouth. The three posterior pairs of legs, which are attached to the annu- 

 lated portion of the thorax, are furnished with a brush instead of a hook at their ex- 

 tremities, and more resemble the abdominal swimming-legs. The tail is expanded into 

 a broad fin. By the nature of its conformation, we see that this animal is adapted both 

 for seizing and holding its prey, as well as for swimming, but not at all for walking. 



Dr. Lakis has published the following observations on the habits of a specimen that 

 he kept alive in a basin of sea- water for two days : "It sported about, and exhibited a 

 boldness rather unexpected. When alarmed it sprang backwards with great velocity, 

 after which it placed itself in a menacing attitude. The prominent appearance of the 

 eyes, their brilliancy and attentive watching, the feeling power of the long antennae, 

 evinced quick apprehension and instinct. I brought a silver spoon near them, which 

 was struck out of my hand with a suddenness and force comparable to that ot an electric 

 shock. This blow was inflicted by the large arms, which were closed and projected 

 in an instant with the quickness of lightning. An apparent anxiety to keep the head 

 and claws in front, made me suspect that the animal lodges its hinder parts in holes or 

 recesses, from which it can strike at its prey or other passing objects." 



The Opossum Shrimps (Mysis] have their branchiae sometimes attached 

 to the abdominal legs, sometimes to the thoracic legs, but they are never en- 

 closed within the carapace. These animals 

 have received the name of Opossum Shrimps 

 from the curious pouch, formed of plates 

 attached to the abdominal legs, in which the 

 female protects both her eggs and young 

 until the latter have attained considerable 

 development. 



The opossum shrimps abound in the nor- 

 thern seas. The Arctic Ocean teems with 

 myriads, forming not troops, but vast clouds, 

 spreading over square leagues of water, and 

 affording sufficient and most nutritive food 

 for the whale, and for the prodigious shoals 

 of salmon that visit the shores of Boothia 

 Fir,. i66.-Orossc.M SHRIMP. during July and August, and upon which 



the inhabitants of that dreary region depend 



in a great measure for their supply of winter provisions. During summer the 

 opossum shrimps absolutely crowd the mouths of the rivers, and there their 

 destroyers revel in a continual feast. 



AMPHIPOD CRUSTACEANS. ORDER AMPIIIPODA.* 



In the succeeding Crustaceans the eyes are sessile, that is, not 

 supported on jointed stems, and consequently motionless. The 

 legs appended to the different segments vary much in their struc- 



* &fj.<pt } am phi, of hvo sorts ; TTOI/S, pous, afoot. 



