MUSEUM OF COMPAEATIVE ZOOLOGY. 269 



d. The existence of dimorphism among the males of the germs Cam- 

 barus, first observed by Agassiz, has been fully discussed by Hagen (No. 

 16), who conjectures from the resemblance of the "second form" males 

 to young individuals and the small development of the internal organs 

 of generation, that they are sterile. In Lupa and some other genera of 

 Brachyura dimorphism occurs in the females, many full-grown specimens 

 having a narrow and acute abdomen, instead of the broad, roundish abdo- 

 men of the normally developed individuals. Agassiz learned from ana- 

 tomical examination that the females with a narrow triangular abdomen 

 were sterile. 



These sterile forms may be properly classed among abnormal varia- 

 tions caused by arrest of sexual development.* 



e. Hermaphroditism. ■ — While numerous cases of hermaphroditic insects 

 have been put on record by entomologists, I can find but two undoubted 

 cases of hermaphroditism among Crustacea outside of those groups in 

 which it is the normal condition, viz. the Cirripeds and parasitic Iso- 

 pods. The first case is that of a lobster (Homarus vulgaris) described 

 and figured by F. Nicholls, in 1730, in the Philosophical Transactions of 

 the Royal Society of London (No. 3 of the bibliographical list appended 

 to this paper). In this specimen the right half of the body was female, 

 the left half male, as regards both internal and external organs. The 

 second case is a similar one of Eubranchipus vemalis, lately described by 

 Gissler (No. 18). 



E. von Martens (No. 14) has published an account of three specimens 

 of Cheraps from Adelaide, with openings in the first segment of the 

 third pair of legs answering to the sexual apertures of the normal female, 

 coexisting with the normal male sexual orifices in the first segment of 

 the fifth pair of legs. An examination of the internal parts showed the 

 coiled vasa deferentia of the normal male opening out through the aper- 

 tures in the fifth pair of legs. No ovary or duct leading to the openings 

 in the third pair of legs was detected. The specimens had lain in alcohol 

 some seven years, however, so that the evidence against the existence of 

 any internal female organs cannot be taken as positive. Similar open- 



XXVIII., 1869). Gegenbaur (Grundziige der vergleichenden Anatomie, 2 t0 Aufl., 

 p. 397, 1870) also excludes the eye-stalk from the series of appendages. 



* Among insects the Phalcena heteroclita [Bovibyx monacha ?], described by 0. 

 F. Mtiller (an imago with the head of the larva), is probably to be explained as a de- 

 formity arising from arrest of development. In other cases recorded of the retention 

 of the larval head by a perfect insect, the head of the imago was probably within the 

 head of the larva, which was not cast off at the time of transformation. See Hagen, 

 On some Insect Deformities, Mem. Mus. Comp. Zool., Vol. II. No. 9, 1876. 



