NO. 1504. .1 M ERIC AN PARASITIC COPEPODS— 1 VILSON. 685 



We find here the same variation in the color and pattern of the pig- 

 ment spots as in the previous subfamily, and the}" furnish equally 

 good means of identification. 



It is even more diflicult to hatch these nauplii and rear them through 

 successive moults than it was in the case of the Caliginse. This is due 

 to several causes. 



Both sexes of the adults in the genus Alehio7i are very active when 

 kept in aquaria, swimming about restlessly all the time. And they 

 have the same pernicious habit as Caligus of crawling up out of the 

 water as far as they can get and remaining there until dead and dried. 

 Again with Caligus^ if the female's egg-strings were nearly or fully 

 ripe, she usually refrained from this suicide until after the nauplii had 

 emerged. But the ripeness of the eggs seems to make no difference 

 with Ale^rion^ and as a consequence it is very seldom that a ]>rood of 

 nauplii can be obtained in captivit^^ The explanation of this conduct 

 may possibly be found in the fact that the genera belonging to this 

 subfamily are extremel}' sensitive to temperature changes in the water. 

 A rise of onl}" a few degrees is quickly fatal, and it usualh' happens 

 that nearl}^ all the specimens obtained during the hauling of a fish net 

 are dead before reaching the laboratory, even though the}' were placed 

 in fresh water and in an absolutely clean receptacle. About the only 

 way they can be kept alive is to change the water so frequently that 

 there can be practically no rise in the temperature. But even then 

 they do not live as long as Caligus or Lejjeophtheiriis, and make very 

 poor aquarium material. This is especially true of the adult females; 

 the males and young females are rather more hardy. 



From this it would naturally be inferred that the life-history is a 

 difficult matter to obtain, but there is still a chance of success because, 

 as soon as the nauplius moults into the metanauplius, it fastens itself 

 at once to its host and there remains until fully developed. Hence a 

 careful search of the host at the proper time is almost sure to yield 

 development stages of the parasite. Fortunately the hosts for the 

 two species of Alehion here presented are the smooth dogfish and the 

 sand shark, two of the most common fish along the Atlantic coast. 

 The eggs hatch during the latter part of June and the first of July so 

 that the best time to look for the development stages is during the first 

 two weeks in the latter n!onth. They may be found anywhere upon 

 the shark's body, but seem to prefer the mid-line of the dorsal surface 

 just in front of the dorsal fins. Frequently they are huddled together 

 in clusters and are so close to one another that there is not room for 

 them all to rest against the skin of the host, and some are obliged to 

 stand out from the surface at a greater or less angle. In such instances 

 they resemble a chalimus very closely since the only part of their body 

 in actual contact with the host is the pair of long second antenna\ and 

 thev float out in the water much as though fastened bv a short frontal 



