PARASITES AND MESSMATES 221 



subfamily. Each individual, when it first attaches 

 itself to a host, presents the characters of the male 

 sex. Later it becomes a female, develops a brood- 

 pouch, and produces eggs. The animals are, in fact, 

 hermaphrodite ; but it is to be noted that the 

 hermaphroditism is of a different kind from that 

 presented by the Cirripedia, since the organs of 

 the two sexes are successively, not simultaneously, 

 developed. Where, as in this case, the male phase 

 comes first in the life-history of the individual, the 

 condition is known as " protandrous " hermaphro- 

 ditism. 



Another large group of parasitic Isopods is the 

 suborder Epicaridea, all the species of which are 

 parasitic on other Crustacea. It is not uncommon 

 to find specimens of the common Prawn (Leander 

 serratus) which have a large swelling on one side 

 of the carapace. If the lower edge of the carapace 

 be raised, it will be seen that this swelling is due to 

 the presence in the gill cavity of an Isopod parasite 

 (Bopyrus squillarum). A closely similar form, found 

 on Prawns of the genus Spirontocaris, is Bopyroides 

 hippolytes, represented in Fig. 71. Other allied 

 species are found on Hermit Crabs and other 

 Decapods. When extracted, the parasite is seen 

 to have a flat and curiously distorted body, with 

 extremely short legs ending in hooked claws. The 

 under-side is generally occupied by a relatively 

 enormous mass of eggs, which is only partly covered 



