350 A HISTORY OF KECENT CRUSTACEA 



Bengal and Borneo a true Rocinela^ and that the genus 

 Rocinela may be regarded as a kind of link between the 

 -^gid^e and the next family. 



Family F. — Cijmothoidce.. 



The members of this family in their advanced stages 

 are distinguished from the ^gidae by the antenna, which 

 are nearly always strongly reduced, without clear distinc- 

 tion between peduncle and flagellum ; by the strongly 

 hooked fingers of the fifth, sixth, and often also of the 

 seventh, pairs of limbs of the pergeon ; and by the absence 

 of ciliation from the pleopods, from the terminal segment 

 of the pleon, and almost always from the uropods. 



By one very curious character in at least some of the 

 genera this family is distinguished, so far as at present 

 known, from all the other families which in its more 

 comprehensive sense the name Cymothoidee includes, as 

 well as from all other Isopods. At a certain period of its 

 life the young Cymothoid of some genera is a male, 

 with three pairs of testes, two rudimentary ovaries 

 internal to the testes, and a paired copulatory organ into 

 which the two vasa deferentia open. After a subsequent 

 shedding of the integument, and when the female glands 

 have been developed at the expense of the gradually 

 diminishing male glands, the now developed marsupial 

 plates become free on the legs of the peraeon, and the 

 copulatory organs are thrown oif. This strange cycle of 

 events was discovered by Mr. J. F. BuUar, and confirmed 

 by Dr. Paul Mayer, the latter showing that self-fertilisation 

 does not occur. As these animals when adult adopt a 

 parasitic mode of life, and cannot therefore roam about in 

 quest of partners, Hansen suggests that the propagation 

 of the species may be materially assisted by the alternation 

 of sex in each individual. The peculiarity has been 

 observed in the genera Cymothoa, Nerocila, and Anilucra. 

 It is not to be assumed as belonging to genera in which it 

 has not been actually remarked, and it is rash to speak of 

 the Cymothoidse as hermaphrodite on one page, and on 

 another to assign to this family species of jFga and 



