THE CRUSTACEA 123 



in Scotland ; and though I have carried out several experiments, 

 I have not as yet been able clearly to establish whether the effect 

 produced is truly hypnotic or due to mild frictional electricity. 

 The passing of mild electric currents along the back and carapace 

 has anything but a soothing effect upon the Lobster. 



The genus Palinurus includes the Common Spiny Lobster 

 (Palinurus vulgaris), sometimes called the Crawfish, which inhabits 

 our western coasts. There are no powerful claws, and the true 

 walking legs are all one-toed at their extremity. The illustration 

 facing page 123 is of a Palinurus from India. The Palinuri pass 

 through a complex metamorphosis, the larva presenting a very 

 curious appearance, so different from the adult that, when first 

 observed and described, it was given the name of Phyllosoma, 

 or " Glass Crab." 



The River Crayfish (Astacus ftuviatilis), according to the experi- 

 ments of Ratke, passes through its earlier metamorphosis in the 

 egg. Although it cannot live in salt or brackish water, yet its 

 geographical distribution is wider than that of any other Crus- 

 tacean ; representative species inhabit the rivers of Europe, India, 

 Japan, North and South America, New Zealand, and Australia. 



The Stoniapoda, or mouth-footed Crustacea, show considerable 

 divergence from the crabs and lobsters. Taking Squilla mantis, 

 the so-called " Mantis Prawn," as an example, the segments are 

 much less coalesced than in the lobster. Those bearing the eyes 

 and antennules are readily separated from the front of the head, 

 and are not covered by the carapace, which only conceals eight 

 segments, whereas in the lobster it extends over fourteen. The 

 gills are no longer attached to the thoracic appendages and 

 enclosed in a branchial chamber formed by the head-shield, but 

 they are transferred from the thoracic limbs to the abdominal 

 swimming- feet. The first thoracic appendages are developed into 

 a pair of robust claws, the terminal joint being furnished with a 

 row of long and sharp recurved teeth, giving the limbs a great 

 resemblance to those of the curious insect called the mantis. 



The Isopoda (equal-footed) are sessile-eyed Crustacea, and their 

 name alludes to the general conformity in size and function of 

 the legs. One group of Isopods, the Oniscida, are familiar to most 

 people under the name of Woodlouse, or Armadillo Bug, the 

 latter name referring to their curious habit of tightly rolling them- 



