NO. 1350. XA TURA L inSTOR Y OF THE ISOPODA—RICIIA RDSON. 3 1 



In thi.s order, with the exception of the Epicarideti, p(>rhup,s there 

 its no greater distinction between the males and the females than in 

 the famih^ Gnathiidte". Owinj^ to these differences, at one time the 

 3'ouno- and the females were inclnded in a separate famil}" from that 

 to Avhich the males were assigned. The relationship between the two 

 forms was definitely established b}^ Mr. Eugene Hesse, although sug- 

 gestions were made by Leach as early as 1814 pointing to this con- 

 clusion. The adult males have powerful mandibles projecting in front 

 of the large quadrangularly shaped head. In the female the mandi- 

 bles are absent and the head is small and triangular. The first gnatli- 

 opods in the male are two-jointed opercular appendages. In the 

 female the first pair of legs lie in a membranous plate supposed to 

 be marsupial in character (Stebbing). 



With the Epicaridea not onl}^ is sexual dimorphism most marked, 

 but the males also differ from the females in the shape of the bod}', 

 which is elongate and always bilaterally sjmmietrical, while the body 

 of the female is usually more or less asymmetrical, and has a ten- 

 denc}' to be circular in outline, and in the fact that the segments of 

 the abdomen may be distinct or fused irrespective of this condition in 

 the female. 



13. ALTERATION OF SEX AND HERMAPHRODITISM. 



The peculiar phenomenon of the alteration of sex occurs among 

 some of the Cymothoidte. The 3'oung male at one period is protan- 

 drous, being provided with rudimentary female reproductive organs 

 within the male reproductive organs. When the integument is shed 

 the female reproductive organs develop at the expense of the male 

 organs, the incubatory lamellee arise at the base of the thoracic legs, 

 and the copula tory organs are thrown off. 



This alteration of sex and temporary hermaphroditism of the pro- 

 tandrous tj^pe has been observed in Cymothoa, Nerocila^ Anilocra, 

 and Icthyoxenos. 



The Cryptoniscian larvfe (males) of the Epicaridea develop into 

 adult males and females, the larva? which are to become females having 

 at one period both male and female reproductive organs. In the fam- 

 ily Cryptoniscida' the males not transformed into females do not pass 

 bevond the form of the Cryptoniscian larvse. With the family Enton- 

 iscida? certain males undergo, while retaining their sex, a metamor- 

 phosis less complete than that of the female, but sufliciently great to 

 give a very different appearance to this second form. Thus the Enton- 

 iscidjc have larval males (complementar}^ males) as well as degraded' 

 adult males, both fertile. It may ))e possible as Girard and Bonnier 

 suggest, that, if the adult degraded male should disappear, one of these 

 complementary males may take its ])la('c and continue its transforma- 

 tion into the adult form. The Cryi)toniscida> have only larval males. 

 The Bopyridae have onl}^ degraded adult males. 



