History of British Eutomostraca. 85 



In stating my opinion of the manner in which we may explain 

 the phenomenon of a " tree within a tree/' without the necessity of 

 referring to the theory of Du Petit Thouars, I do not wish to be 

 understood as asserting this theory to be incorrect. If it is to stand, 

 it will doubtless be one day established upon clear and conclusive 

 experimental proof; but in the meantime it is right for us to be 

 cautious in admitting the explanation of any phenomenon upon the 

 supposition of the theory being true, which may as easily be ac- 

 counted for upon other and well established principles. 



III. — The Natural History of the British Eutomostraca. By 

 William Baird, Surgeon. 



There is no order of insects to which so little attention has been 

 paid by the naturalists of Great Britain, as the Eutomostraca, and 

 there are few, if any, that are more deserving of attentive study. 

 The external appearance of these little interesting creatures, viz. 

 insects enclosed in a testaceous covering, is enough of itself to excite 

 the curiosity, and rouse the interest of the naturalist. A great num- 

 ber of them, indeed, are so like shells, that a person ignorant of the 

 inhabitants would not fail at first sight to call them so ;* and the 

 very singular phenomenon of animals belonging to the class of in- 

 sects, being so covered with a shell, has supplied to Muller the 

 name of Entomostracon, a term derived from two Greek words, sig- 

 nifying " an insect with a shell ;"t a name which this order of in- 

 sects has hitherto maintained, and which has been almost univer- 

 sally adopted by naturalists from Miiller's time to the present day. 

 Previous to the appearance of Miiller's work, the few species which 

 were known, were arranged under one genus, the genus Monocu- 

 lus — and they were so called from their possessing, or appearing to 

 possess, only one eye. Schceffer appears to have proposed the name 

 of Branckiopodes for them, from their feet possessing branchial ap- 

 pendages ; and Muller says he would have preferred this name to 

 that of Monoculus, were it not that several species wanted these or- 

 gans. The species, however, which he mentions are either the Nau- 

 plii and Amymones, not aware that these were but the imperfect 

 young of the genus Cyclops, or the Cythere, which possesses bran- 

 chial appendages attached to the jaws instead of the feet. These 

 facts, however, he was not aware of, and therefore he preferred to 

 either of the above names, that of Entomostracon, — a name which I 



* Muller. f Entomostraca, p. 2. 



