N(>. 1573. PARASITIC COPEPODS— WILSON. 331 



But the males are always as hardy as any of the genera he mentions, 

 and usually when placed with Caligus or LepeoiMlieirus they outlive 

 the latter. 



Hesse's mistakes have probably originated from another fact which 

 has an important bearing on the length of life in these parasites. In 

 the Caligina? the arched carapace acts as a large sucking disk, its 

 margin being pressed close to the surface, made continuous posteriorly 

 by the broad lamina connecting the third legs, and the contact sealed 

 with water and slime. 



The space beneath the carapace is filled with water, and this is 

 often retained for a long time after the surface of the fish has become 

 dried. Living and active specimens have often been obtained from 

 fish whose outer surface and fms had been dried for two or three hours. 

 On the inside of the operculum and in the gill cavity they sometimes 

 remain alive out of water for twentv-four hours after the death of the 

 fish. 



In the Pandarinse the carapace is not thus arched and there is 

 nothing to continue its margin posteriorly; consequently it does not 

 retain the water, l)ut the latter escapes as soon as the skin of the fish 

 dries, just as it does from l^eneath the cover glass on a microscope 

 slide. As soon as the fish dries, therefore, all the Pandarids on its 

 outer surface also quickly die, and they do then drop oft", or can be 

 brushed oft' very easily. For the same reason, while the sharks are 

 being brought ashore these parasites usually become exhausted for 

 want of moisture. And although they may still be alive when 

 removed from the fish they do not live very long afterwards. But 

 given a fair chance, the females are as long lived as any of the fixed 

 parasites, while the males who do retain moisture under their cara- 

 paces in the same manner as Caligus and Trehius are fidly as long 

 lived as the latter. ' 



This sid)family of Pandarina? are thus clearly differentiated from 

 the Caligina^ Trebina^, and Euryphorinse on the one side and from 

 the" Cecropin?e on the other by many distinct peculiarities of morph- 

 ology and lial)its. The most striking differences are to be found 

 perhaps in the males, although the other sex is by no means deficient 

 in them. 



In the Caliginse we find the sexes similar, the male usually smaller, 

 but sometimes larger than the female. The young females, and even 

 the adults when without egg-strings, are as active as the males, and 

 both sexes have retained fully their power of locomotion in spite of 

 their parasitic habits. This equality of the sexes is partially explained 

 by the fact that neither of them carry any dorsal plates on the thorax 

 or genital segment. The family includes one genus, Echetus, in 

 which tlie adult female has become fixed in position, but this is due to 

 the burA-ing of the head and thorax in the flesh of the host. 



