BRITISH FOSSIL CRUSTACEA. 3 
these animals—a ead, a thorav, 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 may be held as corresponding with one of the three regions.” 
Dr. Dana, in his great work’ 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* and Mr. J. O. Westwood * differ but little from 
those of Dr. Milne-Edwards. Mr. Spence Bate* objects even more strongly to the use 
of the names ‘thorax’ and ‘abdomen,’ as applied to Crustacea, than Milne-Edwards, 
and ‘pleon,” 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. he 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 
95 
and recommends instead the terms ‘ pereion 
‘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.’ 
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 adjoiming 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. 
? See ‘Brit. Assoc. Report,’ 1855, by Mr. C. Spence Bate, “On the British Zdriophthalma,” p. 27. 
> C. Spence Bate and J. O. Westwood, on ‘ British Sessile-eyed Crustacea,’ part i, p. 3, 1861. 
* C. Spence Bate, “On the Development of Decapod Crustacea,’ ‘ Phil. Trans.,’ 1858, p. 590. 
> From repatow, to walk about. 
6 From zhéw, to navigate, 
7 The terms ‘head,’ ‘ thorax,’ and ‘abdomen’ are still retained by Entomologists for the class nsecta, 
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.R.S., ‘ Medical Times and Gazette,’ 1857, 
p. 507. 
