38 REPORT — 1855. 



which demonstrates that a fusion of the parts of the leg with the body is no 

 evidence of a more or less perfect type of Crustacea. 



4th. That close exammation shows that, the (so-called) epimerals are 

 not united to the segments in a manner tohich ivoidd be the case if they were 

 merely separated parts of the same segment (Plate XV. fig. 8). — It is but 

 natural to suppose, wlienever, in the structure of a segment, it is necessary 

 that a line of demarcation, from incomplete union by an arrest in the deve- 

 lopment of the whole, must exist, the two separated portions would con- 

 tinue in the same plane. But these coxae articulate with their segments by 

 the length of at most one-half of the width of the segment only, and that 

 upon the inner portion. It is this line of demarcation which splits when 

 the animal throws off its exuviae, and leaves the coxae attached to the 

 legs, a fact which shows that a closer connexion exists between the leg and 

 the scaliform coxa than between the coxa (epimeral) and the body of the 

 animal. 



5th. There are no epimerals where there are no legs. 



6th. Epimerals are not observed in any except the Edriophthalma. 



These two last arguments are negative in their character; but it is at least 

 curious, that if the coxae, are side-pieces of each successive segment, a 

 more perfect development of the segments with the side-pieces takes place 

 posteriorly where the perambulating legs cease to exist. Again, their absence 

 in the Macroura (for we consider it a thing proved that the so-called epimerals 

 appertaining to the carapace are in fact the mandibular segment*) is at least 

 remarkable both in the anterior and posterior portions of the animal. 



Posterior to the perambulating legs, the pleopoda or swimming-feet are 

 attached to the underside of what is commonly called the abdomen, but 

 which we think with more convenience may be called the pleon, being the 

 segments which bear the swimming feet. 



The superior arches of the segments overlie the side of the inferior to a 

 considerable extent, but there are no traces of anything like independent 

 side-pieces or epimerals. 



Taking these several facts into consideration, we are forced to the con- 

 clusion that the epimerals of Milne-Edwards are not lateral pieces of the 

 normal segment, but the first joint of the true legs, and homologize with the 

 coxopodite of the same author in the Brachyura and Macroura, 



In the Amphipoda the coxa is developed into a scale-like form common 

 to the whole order, and is produced to a much greater extent in the four 

 anterior than the three posterior legs. The three last have generally the 

 second joint (basis) developed to assume the scaly appearance which belongs 

 to the anterior coxa. 



In some species, as in Montagua, one or two of the anterior coxae are 

 developed so as to hide the whole of the rest of the inferiorly situated parts 

 of the animal. 



On the microscopic Structure of the Integumentary Skeleton. 



In all Crustacea, from the highest to the lowest, the composition of the 

 tissues is the same. 



From its capability of withstanding the disintegrating power of boiling 

 potash as well as that of the mineral acids, the base of the structure is 

 assumed to be chitine, developed in the form of cells, the hollows of which 

 are filled with carbonate of lime. 



The process of development appears to be analogous to that of the higher 



* Annals of Nat. Hist. July 1855, and in Dana on Crustacea. 



