198 Dr. C. Chilton on the 



the female, and is generally of a paler and less varied colour"*. 

 Budde-Lund gives the dimensions as " Long. 20-28 mm. ; 

 lat., <J 8-10 mm., $ 10-14 mm. ; alt. 3*5-5 mm." f J but, 

 so far as I can ascertain, gives no difference beyond this one 

 in width, while Sars, on the other hand, speaks only of 

 a difference in length, saying, " Length of adult female 

 20 mm., of male up to 28 mm." \ Dollfus, in his paper on 

 the distribution of the genus Ligia, says : — " Les femelles, 

 plus petites, sont ge"nereusement plus nombreuses que les 

 males " §. 



If we turn to other species of Ligia, our recorded know- 

 ledge of the differences between the male and female does not 

 seem to be much more complete. Budde-Lund gives very 

 brief descriptions of the first pair of legs in the male in Ligia 

 occidentalism L. cinerascens, L. exotica, L. O/fersii, and 

 L. dentipes, but does not state in what respect these ap- 

 pendages differ from those of the female ; in the case of 

 L. exotica he mentions also that in the male the uropods are 

 three fourths the length of the body, but in the female 

 scarcely two thirds ||. Dollfus has also drawn attention to 

 the differences between the sexes in L. exotica as regards the 

 first pair of legs, and has figured the extremities of these legs 

 in the typical form and also in specimens from Bermuda, for 

 which he has established the variety hirtitarsis "fl. 



In the nearly allied family of the Trichoniscidse we find 

 that sexual differences have been described in Trichoniscus 

 roseus by Max Weber** and Sars ft among others, though, in 

 keeping with that fickleness which so often characterizes these 

 differences, here it is the seventh pair of legs, and not the 

 first, that is specially modified in the male. 



Dollfus has described and figured a remarkable enlarge- 

 ment of the extremity of the first, third, and fourth legs in 

 PMloscia anomala, and has given references to similar modi- 

 fication in other species of Philoscia. In the case of P. anomala, 

 since the enlargement was found in some of the males only, 

 he thinks that it is perhaps a temporary character fully 



* l British Sessile-eyed Crustacea,' ii. p. 446. 



t ' Crustacea Isopoda Terrestria,' p. 2G0. 



X ' Crustacea of Norway/ II. Isopoda, p. 156. 



§ ' Feuille des jeunes Naturalistes,' ser. iii. no. 278. 



|| ' Crustacea Isopoda Terrestria,' pp. 264-268. 



•II " Isopodes terrestres du ' Challenger,' " Socie'te' d'Etudes scientifiques 

 de Paris, xii. e annee, p. 8. 



** " Anatomisches iiber Trichonisciden," Archiv fiir mikroskop. Anat. 

 Bd. xix. p. 624 &c. 



ft ' Crustacea of Norway,' II. Isopoda, p. 163. 



