These "psychically decadent" individuals appear to represent the entire male sex of a bisexual species, and become unnecessary owing to the grafting of hermaphroditism on the female sex.
To be an Arachnidan characteristic. But they cannot be affiliated with this order on account of the total suppression of the abdomen, of their hermaphroditism and of the communication that exists between the generative organs and the alimentary tract.
(For fuller information upon the sense-organs see Hydromedusae.) Medusae are nearly always of separate sexes, and instances of hermaphroditism are rare.
Hermaphroditism is secondary, and occurs in one sub-class of Gastropoda, in some Lamellibranchs, and in one sub-order of Amphineura.
Apart from certain doubtful and possibly abnormal instances among Phyllopoda and Amphipoda, the only exceptions are the sessile Cirripedia and some parasitic Isopoda (Cymothoidae), where hermaphroditism is the rule.
In spite of the opinion of some distinguished zoologists to the contrary, it seems most probable that the separation of the sexes is in this case a secondary condition, derived from hermaphroditism through the intermediate stage represented by the species having complemental males.