﻿BRITISH FOSSIL CRUSTACEA. 3 



these animals — a head, a thorax, and an abdomen ; and from this custom we shall not 

 depart, although we must avow that these denominations are only derived from very 

 clumsy views, and are calculated to convey false impressions in regard to the nature and 

 composition of the parts so named, by leading the mind to liken them to the grand 

 divisions entitled head, thorax, and abdomen, in the Vertebrata. 



" Nevertheless, with the exception of the objectionable names, the division of the body 

 into three regions is not less a fact as regards the organization of the Crustacea; and the 

 one and twenty rings of which, as we have said, their body consists in the type to which 

 every member of the class may be referred, are generally found divided into three equal 

 series of seven, each of which maybe held as corresponding with one of the three regions." 



Dr. Dana, in his great work 1 on the Crustacea, distinguishes this class from the 

 Insecta by its possessing a cephalothorax and an abdomen; the former having 14 

 segments, the latter 7. 



The views of Mr. C. Spence Bate 2 and Mr. J. O. Westwood ? differ but little from 

 those of Dr. Milne-Edwards. Mr. Spence Bate 4 objects even more strongly to the use 

 of the names ' thorax ' and ' abdomen,' as applied to Crustacea, than Milne-Edwards, 

 and recommends instead the terms 'pereion' 5 and f pleon,' 6 as less calculated to mislead 

 the student as to the homologies of the divisions of the body. But any names, however 

 well devised, must fail to meet all the requirements of a class so diversified in its various 

 orders as this. The frequent interblending of a part, or the whole, of the segments of 

 the second division of the body with the head of the animal, necessitating a term like 

 ' cephalothorax ' to express it, has been the chief reason for their retention, and long 

 usage must command a certain amount of respect even for a " clumsy" term. 7 



Prof. Huxley, in his lectures on the Crustacea? divides the body into 6 cephalic, 

 8 thoracic, and 6 abdominal segments or somites. He considers the caudal segment, or 

 telson, not to be a segment, properly so called, but a peculiar median appendage ; thus 

 reducing them to 20 in all. 



We give these several views on the adjoining page, and shall discuss their applica- 

 bility as we proceed. 



1 'United States Expl. Exped. 1852, Crustacea,' by J. D. Dana, vol. xiii, part i, p. 21. 



2 See 'Brit. Assoc. Report,' 1855, by Mr. C. Spence Bate, "On the British Edriopkthalma," p. 27. 

 s C. Spence Bate and J. 0. Westwood, on ' British Sessile-eyed Crustacea,' part i, p. 3, 1861. 



4 C. Spence Bate, " On the Development of Decapod Crustacea,' ' Phil. Trans.,' 1858, p. 590. 



5 From Trepatow, to walk about. 



6 From 7r\ew, to navigate, 



7 The terms ' head,' ' thorax,' and ' abdomen' are still retained by Entomologists for the class Insecta, 

 although some of the objections to their use in the Crustacea also hold good in that class. 



8 "Lectures on the Crustacea," by Prof. T. H. Huxley, F.B.S., 'Medical Times and Gazette,' 1857, 

 p. 507. 



