ISOPODA OF THE ' LIGHTNING ' AND OTHER EXPEDITIONS. 105 



the carapace. The genus IpMnoe has a carapace crested with serrse. the pleon is greatly 

 elongated in the female, and the lower antennse are quite rudimentary, consisting of a basal 

 and an extremely minute second joint; the pleon is without any pleopods. The adult 

 male has no spines on the crest of the carapace ; the lower antennse are of extraordinary 

 length, consisting of a well-developed five-jointed peduncle and a very long filament, 

 which extends the whole length of the body, and is tucked away between the bases of 

 the five pairs of largely-developed and well-ciliated pairs of swimming pleopods, and 

 unquestionably are used as organs of sensation. Now, ordinarily, as the male approaches 

 maturity, not in one moult, but in two or more, as is commonly the case in males among 

 Amphipoda as well as Isopoda, the antennee become large and the pleopods more deve- 

 loped ; and examples are commonly found with imperfect pleopods present but naked, 

 and the carapace still retaining the serrated crest characteristic of the female. At the 

 final moult, when the pleopods attain maturity and are densely ciliated, and all other 

 features of the specialized male are developed, the carapace loses its serrated crest. We 

 have examined a large number of the species most common on our coast, Iphinoe tri- 

 spinosa, Goodsir, but have not as yet met with & full y-developed male retaining the serrse 

 of the carapace. My friend Prof. G. O. Sars \ however, has figured two forms of the 

 male in an allied species, Iphinoe serrata, Norman, the one being the normal male with 

 smooth carapace, the second (pi. xxviii. fig. 3) with a serrated crest, as in the female, 

 constituting a " forma altera maris." 



It is possible that this second form may correspond to the state of Cambarus, which, 

 after the discharge of the sexual functions, moults, and retakes a form which approaches 

 nearer to that of the female. 



In the case of the Isopodan genera Leptochelia and Anceus in the moult which pre- 

 cedes sexual intercourse, grasping-organs of enormous size are developed, which require 

 so large a space of the animal's body for their articulation, that the mouth is to such an 

 extent encroached upon, that the mandibles and maxillae are altogether aborted, and 

 the Crustacean thus loses all power of taking food. It seems obvious, therefore, that 

 it cannot long exist in this condition, and that one of two things must take place. 

 Either, having discharged its sexual functions, it must soon afterwards die, or it must 

 moult again, and at that moult cast off its exaggerated limbs, and retake such as are of 

 moderate dimensions, together with the mouth-organs. Mr. Faxon's discovery seems to 

 give strength to a view that the latter of these events may take place in the life-history 

 of these very interesting male Crustaceans. 



' G. 0. Sars, " Nye Bidrag til Kundskabeu om Middelhavets Invertebratfauna. — II. Hiddelhavets Ciimaceer," 

 Archiv for Mathematik og Naturridenskab, 1878. 



