MOKPHOLOGY 01' THE COPEPODA. 297 



structure of the antennae and oral organs from the correspond- 

 ing females ; it is only in the formation of the ja\y-feet that 

 they present any considerable difference. Whilst in them the 

 arm-like clasping organs of the female are wanting, there 

 succeeds to the first pair of maxillary feet, which are like 

 those in the female, a second pair, which correspond with the 

 preceding in structure (fig. 6/), and in their position supply 

 the place of the coalesced arm-pair. Moreover, it may be 

 remarked (besides KoUar), V. Nordmann has made us ac- 

 quainted with young forms of Achtheres and TracheliasteSy 

 which, besides the first antennae, are provided with three pairs 

 of clasping-feet,tlie second antennae, and the four maxillary feet. 

 From this the distinguished observer concludes that the first 

 pair is transformed into the jaws (second antennae), whilst 

 the last pair grow together at the point, and become the arm- 

 like appendage. The mandibles and palpi on the conical 

 beak have unfortunately been overlooked ; but, as I perceive 

 from Kollar's figures, they are always present at this stage. 



From these considerations, if we now endeavour to establish 

 characters for the interesting family of the Lernaeopoda, in 

 the first place we must give up as a character the absence of 

 any segmentation of the body, which has been taken by 

 Milne-Edwards as a distinction between the Chondracanthoi, 

 Lernceopoda, and Lernaee, and the Siphonostomata, since in 

 LeriKBopoda Galei the first two thoracic rings are manifest 

 as distinct segments ; and, besides this, in all the genera the 

 anterior division of the cephalo-thorax appears sharply 

 defined from the posterior. We have, indeed, to consider 

 the slight, incomplete articulation of the body, the more or 

 less complete fusion of the rings ; but, together with this, 

 especially the abortive condition of the abdomen, the absence 

 of all thoracic limbs, the coalescence of the second jaw-feet 

 in the female into an arm-shaped organ of attachment, as 

 well as the conformation of the oral organs allied to that 

 existing in the Siphonostomata. It appears to me, also, that 

 the structure of the second antennae, which project in the 

 form of pincer-like clasping-hooks on the sides of the frontal 

 region, is common to all the genera and species belonging to 

 this subdivision. 



Lastly, in the family of the Lernaeae we meet with the last 

 and lowest stage in the morphological development of the 

 body and of the limbs existing in the group of parasitic 

 Crustacea, or even, it may be said, in the whole type of the 

 Arthropoda. It is true that, according to V. Nordmann and 

 Milne-Edwards, vestiges of thoracic members are present in 

 some species, as, for example, Peniculus and Penella, and 



