740 PROCEEDINaS OF THE NATIONAL MUSEUM. vol xxv. 



some provision whereby the parasite could cling more lirmly to its 

 host. This change resulted first in the further development of such 

 appendages as were already adapted for clinging, such as the maxilli- 

 peds, etc., and the claws and spines upon these appendages were 

 increased in size and strength or modified in form so as to be still 

 better suited for such a purpose. 



Then other appendages, such as the antenna?, etc., which were not 

 originally or normally adapted to clinging or grasping, l)ecame grad- 

 ually so greatly modified as to serve very poorly their original pur- 

 pose, but are almost entirel}^ given up to the acquired function. Such 

 a condition as this we do find admirabl}' illustrated in several of the 

 so-called ''unarmed" species of Doloj)--^, such as ninarinii, longl- 

 ea 11(1(1, etc. 



As a further means toward this same end, prehension, the ventral 

 surface of the carapace is next covered with spines pointing ))ackward, 

 a condition well illustrated by the so-called "armed" species of Dolops^ 

 such as reperta, striata^ etc. 



The wound and the subsequent irritation caused l)y forcing the 

 enlarged claw-like hooks on the antenna and the first maxillipeds into 

 the flesh of the host must produce a copious flow of blood for the par- 

 asite. But these creatures are naturally very active, and they swim 

 about freely, so that the forcing of their claws into their host, together 

 with the subsecjuent withdrawal of them ever}' time they wished to 

 change their location, would impede considerably their freedom of 

 motion. Consequently we next find the anterior maxillipeds entirely 

 altered in structure, though still retaining their same function. 



The terminal joints, with their stout hooks, are graduallv alisorbed, 

 and in their place appear the circular sucking disks. These, through 

 the ci'eation of a partial vacuum by means of nuiscular action, cling as 

 firndy to the skin of the host as did the claws, and they possess the 

 further advantage that their hold can be taken or loosened instantane- 

 ously, thereb}' enabling- the copepod to move about quickly over its 

 host's body or to leave it and swim away. 



This condition we find realized in the new genus Choxojhltis^ recently 

 descril)ed by Thiele (1901), where the anterior maxillipeds are modiHed 

 into sucking disks, but otherwise the appendages are the same as in 

 the " unarmed " species of D(>l(jps. Curiously enough, there is also in 

 this genus a complete suppression of the spines on the ventral surface, 

 and there are no anterior or prehensile antennae. Just what signifi- 

 cance this may have in regard to the sequence of modifications can 

 only be determined after the early development of the genus has been 

 worked out. 



But, while this change from claws to sucking disks in the anterior 

 maxillipeds increases the facility of movement, it also deprives the 

 parasite of his chief means of getting food. The sucking disks are 



