238 CRUSTACEANS. 



and variety abound in the sea. Some species, indeed, are profusely dis- 

 tributed, though others are comparatively rare. The dwelling of certain 

 animals is sometimes such, as to induce us to involve a contradiction in 

 calling them common, when, in foct, they prove quite the reverse. 



It is extremely doubtful whether, according to modern ari'ange- 

 ments, the proper position is assigned to this animal. Formerly the com- 

 mon Asellus followed the Crustaceans, in accordance with the Linnsean 

 system ; but the object of that system, now abandoned, was to facilitate 

 the acquirements of the student, by the utmost order and simplicity. 



Although the species about to be described is said to be common 

 by various authors, as its name indicates, I have found it extremely rare. 



There is one place, however, in the immediate ^acinity of the City 

 of Edinburgh, a pond at Eed Braes, where it abounds in remarkable 

 profusion ; therefore this must be a situation most congenial to its na- 

 ture, which will always regulate, restrain, or promote the numbers of an 

 animal. Being surrounded by trees, whose decaying leaves cover the 

 bottom of the pond, neither food nor shelter is wanting. If I have 

 seen it elsewhere, it has been only in solitary specimens. 



To the naked eye this is a coarse, and rather an ugly object, if any 

 product of the creation can be truly deemed such from the hands of the 

 Creator, for that is a point whereon I entertain many scruples. — Fami- 

 liarity, besides, reconciling us to all things. 



The curious structure of the Asellus, unintelligible by our imperfect 

 organs, is illustrated in an admirable manner by the microscope, always 

 a ready auxiliary in revealing the secrets of nature. This is shewn very 

 impressively by Plate LXV. tigs. 1, 2 ; the first the natural size, the 

 second an enlarged view of the animal, sufficiently descriptive of its ap- 

 pearance. In Scotland it is called the Slater. 



Among a group of Aselli many occur under a great disparity of or- 

 ganic dimensions. None exceed six lines in length, by little above half 

 a line in breadth, then declining to those most diminutive. 



This creature is of flattened form, with two eyes, four antennae, 

 fourteen limbs, and a forking style from each side of the last segment, 

 all constituting the external organs. 



