316 
BRITISH EN TOM 0 STR A 0 A . 
f 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 Loudon’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, 8fc . — The form of the animals 
belonging to the Lerneadse is very variable. “ Respecting 
this,” says Kroyer,* £C 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. 174. 
