NO. 1350. NATURAL HISTORY OF THE ISOPODA— RICHARDSON. 63 



A male in the crvptoniscan staj»"e was found on ono immatui-e female 

 (in first post-lar\'al .stage). 



Thoracic processes of f id} dt female. — In the adult female the thoracic 

 processe.s ma}'^ be quite reduced. In some specimen.s these proce.s.ses 

 are well developed, though never in all the specimens examined were 

 they found as long as in the very young female or as in the figure 

 given by Dana of the adult female. In other specimens these proc- 

 esses are very small, and yet in many they were not even present. 

 Not onl}^ is this variation found in specimens taken from different 



'6 



Fig. 39. — .\rgeia puhettensis. a, dorsal view of immature female; h, ve.ntral view of same. 



Xl4i. 



species and genera of host, but it was also true of those found on the 

 same species and genus of host. As a result of this observation on a 

 large number of these forms, the conclusion must be maintained that 

 these thoracic processes, well developed in the young female, of vary- 

 ing size and shape and sometimes so reduced as to be practically absent 

 in the adult female, have no specific value whatever. Giard and Bon- 

 nier" have described their function as organs of fixation, which seems 

 a reasonable conclusion and one capable of explaining why so much 

 variation occurs in this respect with each individual parasite. 



The following paragraph is taken from the above quoted authors: 



The " lames epimeriennes (nos lames pleurales)" have, as we have already said, 

 l)iit a very slight morphological importance. They are organs of fixation developed 

 to assure the position of the parasite in the l)ranchial cavity of the host and to pro- 

 tect it against the gill sweepers. Their form, their number, tiieir dimensions are 

 therefore only in accord with the peculiarities which the branchial cavity presents, 

 and one knows nothing more variable in the decapod Crustacea than the organ- 

 ization of the branchijie * * * the presence of pleural lamelh^e in these animals 

 is evidently simply a fact of adaptive convergence. 



'' Contributions a I'^tudedes Bopyriens. Travaiix de I'lnstitut zoologi(]ue de Lille 

 et du Laboratoire de Zoologie maritime de Winicreux, \ , 1SS7, p. 61. 



