90 REPORT — 1876. 



economy of the animal can, I think, be demonstrated in the habits of theii- 

 life — a circumstance which, I think, can be shown in the slight variation of 

 their structure in the adult stage from that of the larval form, to depart in 

 the anterior members towards the mandibular form, and posteriorly to put 

 on conditions most consonant with the usefulness of the succeeding appendage ; 

 that is, while the anterior ones feebly approximate the mandibular form, the 

 posterior have attached to them parts resembling immature branchial organs. 

 These seven pairs of appendages are all that belong to the cephalon or head ; 

 and it appears to me that, however closely any of those that succeed may be 

 associated with them in functional purposes, they are homologically distinct, 

 and, as members of separate portions of the body, they should be named 

 and distinguished in a scientific nomenclature more in accordance with their 

 homological relationship than with their functional power. 



The next pair of appendages is the first that belongs to the pereion or 

 thorax in the Crustacean typo of animals. It is the eighth pair in posterior 

 rotation, but is generally named by authors according to its relation to the 

 mouth. It is the 2'>^^^^ptognatlie of Milue-Edwards's more recent nomenclatvu'e, 

 the second pair of mdcJioires auxiliaires of Savigny, and the second pair of 

 maxUlipeds or foot-jaws of most carcinologists. It is the fourth siagnojoodos 

 according to Professor Westwood's suggestion, and the fii'st pair of gnatlio- 

 poda of the 'History of British Sessile-eyed Crustacea,' according to the 

 nomenclature of the author of this report. 



This multiplication of names for a single appendage, signifying, as they 

 severally do, various affinities, is by no means flattering to the students of 

 Crustacea; but, to a large extent, it occurs from the circumstance that while 

 one anatomist has contemplated the animal in the adult and higher concen- 

 trated forms, others have contemplated it in the more imperfect types. It 

 is therefore the object in this report to bring together these several and 

 various discrepancies, and demonstrate the relationship) of jiarts through 

 their various degrees of growth and change, and retain by one fixed name 

 the same part however it may vary in structure or functional conditions 

 through all stages of variation in Crustacean life. 



• In Crustacea the eighth pair of appendages in the structure of the ani- 

 mal is the first pair that belongs to the body. In the Brachyura it 

 exists in the same type as is found in the zoea or larva form (fig. 29), 

 from which it varies only in the more robust character of some of the 

 joints of which it is constructed (PL III. fig. 30). In this state it varies in 

 form and degree only within a limited range, gradually becoming more pedi- 

 form in character as we examine it through the Macrura (PL III. fig. 31) in 

 the descending order until we reach SquUla (PL III. fig. 32), where we find 

 it developed as a large and important organ that gives a decided and distin- 

 guishing feature to the animal. Through this genus we are led to the 

 Eriophthalmia (PL III. fig. 33), among which we find that in the Amphipoda 

 it is formed on the same type as in SqiiiUa, but gradually approaching in its 

 general characteristics and appearance those of the succeeding pairs of legs, 

 until in the Isopoda it is in most families uniform with them. 



Thus we see that not only in their relation to the body of the animal, but 

 also in their most general appearance and affinities they are part of the 

 game system of appendages as those posterior to them, and that their relation 

 to those anterior arises from that crowding together of parts in the higher 

 types of Crustacea that forces an abnormal form as the result. 



This fiair of appendages, as being the first attached to the " pereion " or 

 body of the animal, may with consistency be called, as it reaUy is, the 

 first pair of pereiopoda. But throughout the higher Crustacean forms the 



