Ou the Life-History and Development of the Genus Myzostoma. 571 



male form wliere two or more hermaphrodites are sitting together ou a 

 Comaüila, and this fact is worthy of notiee, for if Prof. Graff's expla- 

 iiation were correct, they would oceur oftenest, where seyeral M. gla- 

 hrimi are parasitic on one Crinoid. Very rarely have I found two males 

 on one liermaplirodite form (fig. 30). The hermaphrodite forms on 

 which the males sit are always large, and eontain numerous fully de- 

 veloped ova. In many cases also fully developed spermatozoa , but in 

 some cases the testes are small and not well developed and thus the 

 hermaphrodite becomes physiologically to all intents and purposes 

 female. In these hermaphrodites the vasa deferentia are ne ver absent. 

 Even when the testes in these cases are well developed and eontain 

 ripe spermatozoa, they show nothing approximating the number of 

 spermatozoa found in the much smaller males. 



I have found these males at all times between November and April. 

 Graff thought these so-called Junge occurred oftenest in Trieste in 

 autumn, whether there is any real periodicity in their occurrence is 

 doubtful. — More probably they occur at all times — at any rate in 

 Naples. 



The discovery of males with hermaphrodites in this group is not 

 without interest. Their occurrence was known among Arthropoda 

 where Darwin ^ described them as complemental males under the Cir- 

 ripedia^ but their origin and meaning remained an enigma to him. It 

 will be interesting before discussing the whole question to examine the 

 results to which Darw^in arrived among the Cirripedia. 



He found that in the genus Ihla the ordinary individuals were not 

 hermaphrodites, but females in whose body sac one or two little worm- 

 like bodies occurred. These proved to be the males of the species 

 examiued, Ihla Cumingii. 



Such a thing had nothing very much unusual in it. But he found 

 in another genus of Cirripedes , ScalpeUum , these little »complemental 

 males« in much greater numbers , and in this case the individuai in 

 which they occurred was hermaphrodite. 



In all, four different cases are described by Darwin as occurring 

 within the limits of the genus Ihla and ScalpeUum. 



These are : 1) a female, Ihla Cumingii, with a male er rarely two 

 perman^ntly attached to her, protected by her, and nourished by any 

 minute animals which may enter her sack ; 2) a female ScalpeUum or- 

 natum with successive pairs of short-lived males , destitute of mouth 



1 Darwin, Monograph of the Cirripedia. Vol. I. 



