Sexual Characters ofLv^x^x oceaiiica. 199 



developed only at the pairing-season*. Later on he described 

 a similar modification in the first pair of legs in the male of 

 Pliiloscia variegata from Venezuela f. 



Probably similar differences will be found to exist in many 

 other species of Terrestrial Isopoda, and may have been re- 

 corded; but the above references, for <^o\\\i of which I have 

 to thank the Rpv. T. R. II. Stebbing and Monsieur Adrien 

 Dollfus, are all that I have so far been able to find on the 

 subject. 



In Ligia oceanica tlie male wlien fully adult is, as has beeti 

 already stated by other authors, usually larger than the 

 female ; but though the female, when its brood-pouch is fully 

 distended with eggs or young, may be wider in proportion 

 than the male, this does not seem to be always so, for in the 

 case of the specimens specially examined and drawn for this 

 paper the male was 25 millim. long and 12 millim. wide, 

 while the female was 24 millim. long but only 10 millim. 

 broad, though the brood-pouch was well filled with eggs. 



The outer antennte show some slight diff-^rences in the two 

 sexes, being appreciably stouter in the male both in the peduncle 

 and in the flagellum. This will be seen on comparison of 

 figs. 1 ant and 2 ant (PL VIII.), which are taken from male 

 and females of nearly the same size, and are magnified to 

 approximately the same amount. In the female the antennaB 

 are sometimes slightly more spiny than in the male, but I 

 have not been able to make out any constant differences in 

 the proportions of the various joints. I was in the museum 

 of the Dundee University College when the greater stoutness 

 of the antennaj of the male was first noticed, and Mr. Caiman 

 and I then went over a large number of specimens in the 

 collections of the museum, and found that in fully adult 

 specimens we could correctly separate the males and females 

 by the characters of the antennae alone ; in smaller and 

 immature specimens the differences are naturally not so 

 marked. 



When we turn to the appendages of the perajon we find 

 that there are slight modifications in the male in the first, 

 second, and third pairs. As these three pairs differ from one 

 another only in the fact that each is \qxj slightly longer than 

 the preceding, I have drawn only the second pair (fig. Iprp^). 



* L. c. p. 5. 



i" Extrait cles ' Annales cle la Soci^t(5 Entoniologique de France/ 



vol. Ixii. p. 343. 



15* 



