IBLA AND SCALPELLUM. 281 



have stated regarding the affinities of the latter, are here 

 quite applicable. It is singular how much more alike 

 the parts of the mouth and the cirri of these two com- 

 plemental males are, than the corresponding parts in the 

 two hermaphrodites : this no doubt is due to the two males 

 having been arrested in their development, at a corre- 

 sponding early period of growth. Several of the characters, 

 by which the hermaphrodite S. vittomm so closely ap- 

 proaches, and almost blends into the genus Pollicipes, — 

 such as the thicker cirri, with the intermediate tufts of 

 bristles, the small second tooth of the mandibles, and 

 the little brush-like prominence on the maxillae, — are not 

 in the least apparent in the complemental male. 



SUMMARY ON THE NATURE AND RELATIONS OF THE MALES 

 AND COMPLEMENTAL MALES, IN IBLA AND SCALPELLUM. 



Had the question been, whether the parasites which I 

 have now described, were simply the males of the Cirripedes 

 to which they are attached, the present summary and dis- 

 cussion would perhaps have been superfluous ; but it is 

 so novel a fact, that there should exist in the animal king- 

 dom hermaphrodites, aided in their sexual functions by 

 independent and, as I have called them, Complemental 

 males, that a brief consideration of the evidence already 

 advanced, and of some fresh points, will not be useless. 

 These parasites are confined to the allied genera Ibla and 

 Scalpellum ; but they do not occur in Pollicipes, — a genus 

 still more closely allied to Scalpellum ; and it deserves 

 notice, that their presence is only occasional in those 

 species of Scalpellum which come nearest to Pollicipes. In 

 the genera Ibla and Scalpellum, the facts present a singular 

 parellelism; in both we have the simpler case of a female, 

 with one or more males of an abnormal structure attached 

 to her ; and in both the far more extraordinary case of 

 an hermaphrodite, with similarly attached Complemental 

 males. In the two species of Ibla, the complemental and 

 ordinary males resemble each other, as closely as do the 

 .corresponding hermaphrodite and female forms ; so it is 



