316 BRITISH ENTOMOSTRACA. 



' Nov. Act. Acad. Nat. Cur./ 1821 ; Mayor, in the 

 'Nouv.Bull.de la Soc. Philomath.,' 1824; Lesueur, in 

 the 'Journal of the Acad. of Nat. Sc. of Philadelphia,' 

 1824; Scoresby, in his 'Arctic Regions, 1820;' Grant, 

 in Brewster's 'Edin. Journal of Science,' 1827 ; Retzius, 

 in the 'Kongl.Vitensk. Acad. Handling., 1829; Johnston, 

 in London's 'Mag. of Nat. Hist.,' 1836, and various 

 other naturalists, have all added more or less to our in- 

 formation, and extended our knowledge of the species of 

 these animals ; while M. Edwards, in his ' Hist. Nat. 

 Crust.,' has collected all the species together, and arranged 

 them in their respective families and genera. 



Anatomy and Physiology, &fc. The form of the animals 

 belonging to the Lerneadse is very variable. " Respecting 

 this," says Kroyer,* " it is not easy to say anything 

 general. The remark only forces itself upon every ob- 

 server, that the exterior of these animals is often so highly 

 fantastical, that we are disposed to admire the freaks of 

 nature in bringing forth such forms. But it is evident, 

 that when continued observations and investigations have 

 put us in possession of the condition of these forms, we 

 shall see here, as everywhere else, that singularity resolves 

 itself into regularity." 



Eor the most part the skin, or external envelope, is soft 

 and flexible, but there are many species in which it is 

 somewhat of a cartilaginous consistence. Nordmann has 

 discovered that it consists of a threefold structure ; an 

 external layer, tolerably firm and elastic ; next, a very 

 loose and soft cellular tissue ; and finally, a third layer, 

 composed of a number of muscular fibres crossing each 

 other in length and breadth, and having, in consequence, 

 a reticulated appearance. 



We can generally trace, more or less distinctly, a 

 division of the body into two parts ; the first of which, 

 the smaller of the two, forms the head, and the other the 



* Tidsskrift, p. 171. 



