IBLA AND SCALPELLUM. 291 



fertilising some of the ova, as the pollen of many dioecious 

 plants, trusted to the wind, has of reaching the stigmas of 

 the female plants. Regarding the final cause, both of the 

 simpler case of the separation of the sexes, notwithstanding 

 that the two individuals, after the metamorphosis of the 

 male, become indissolubly united together, and of the much 

 more singular fact of the existence of Complemental males, 

 I can throw no light ; I will only repeat the observation 

 made more than once, that in some of the hermaphrodites, 

 the vesiculae seminales were small, and that in others the 

 probosciformed penis was unusually short and thin. 



Viewing the parasitic males, in relation to the structure 

 and appearance of the species to which they belong, they 

 present a singular series. In S. Peronii and S. vittomm, 

 the internal organs have the appearance of immaturity; 

 the shape of the capitulum is specially modified for its 

 reception between the scuta of the hermaphrodite, and 

 several of the valves have not been developed. This 

 atrophy of the valves, is carried much further in S. ros- 

 tratum. In Ibla, many of the parts are embryonic in 

 character, but others mature and perfect ; some parts, 

 as the capitulum, thorax, and cirri, are in a quite ex- 

 traordinary state of atrophy ; in fact, the parasitic males 

 of Ibla consist almost exclusively of a mouth, mounted on 

 the summit of the three anterior segments of the 21 normal 

 segments of the archetype crustacean. In the males of 

 the first three species of Scalpellum, some of the cha- 

 racters are embryonic, — as the absence of a mouth, the 

 presence of the abdominal lobe, and the position of the 

 few existing internal organs ; other characters, such as 

 the general external form, the four bead-like valves, the 

 narrow orifice, the peculiar thorax and limbs, are special 

 developments. These three latter parasites, certainly, 

 are wonderfully unlike the hermaphrodites or females to 

 which they belong ; if classed as independent animals, they 

 would assuredly be placed not in another family, but in 

 another Order. When mature they may be said essentially 

 to be mere bags of spermatozoa. 



