282 SEXUAL RELATIONS OF 



with two sets of the species of Scalpellum. But the males 

 of Ibla and the males of Scalpellum certainly present no 

 special relations to each other, as might have been expected, 

 had they been distinct parasites independent of the animals 

 to which they are attached, and considering that they 

 are all Cirripedes having the same most unusual habits. 

 On the contrary, it is certain that the animals which I 

 consider to be the males and complemental males of the 

 two species of Ibla, if classed by their own characters, 

 would, from the reasons formerly assigned, form a new 

 genus, nearer to Ibla than to the parasites of Scal- 

 pellum : so, again, the assumed males of the three latter 

 species of Scalpellum would form two new genera, both 

 of which would be more closely allied to Scalpellum, 

 than to the parasites of Ibla. With respect to the 

 parasites of the first three species of Scalpellum, they are 

 in such an extraordinarily modified and embryonic condi- 

 tion, that they can hardly be compared with other Cirri- 

 pedes ; but certainly they do not approach the parasites 

 of Ibla, more closely than the parasites of Scalpellum ; and 

 in the one important character of the antennae, they are 

 identical both with the parasitic and ordinary forms of Scal- 

 pellum. That two sets of parasites having closely similar 

 habits, and belonging to the same sub-class, should be 

 more closely related in their whole organisation to the 

 animals to which they are respectively attached, than to 

 each other, would, if the parasites were really distinct and 

 independent creatures, be a most singular phenomenon ; 

 but on the view that they differ only sexually from the 

 Cirripedes on which they are parasitic, this relationship is 

 obviously what might have been expected. 



The two species of Ibla differ extremely little from each 

 other, and so, as above remarked, do the two males. In 

 Scalpellum the species differ more from each other, and so 

 do the males. In this latter genus the species may be 

 divided into two groups, the first containing S. vulgare, 

 S. ornatum and S. rutihim, characterised by not having a 

 sub-carina, by the rostrum being small, by the constant 

 presence of four pair of latera, and by the peculiar shape 



