PARASITES AND MESSMATES 223 



pletely known. When hatched from the egg, the 

 free-swimming larvae have a short and broad body, 

 and, as in other Isopod larvae, have only six instead 

 of seven pairs of legs. A later larval stage, just 

 before attachment to the final host, has a long 

 narrow body and the full number of legs. It has 

 lately been shown, however, that, in all probability, 

 between these two free-swimming stages there inter- 

 venes a stage in which the larvae is temporarily 

 parasitic on certain Copepoda. Further, some of the 

 Epicaridea, like the Cymothoinae described above, 

 are protandrous hermaphrodites, developing the male 

 organs when in the last larval stage, and passing 

 into the female phase after they have become attached 

 to the host. In Bopyrus and many other genera, 

 however, there is no evidence that the males ever 

 develop into females. 



Some of the most remarkable Epicaridea are those 

 belonging to the family Entoniscidae, which are para- 

 sitic on Crabs. In these the parasite penetrates from 

 the gill chamber into the interior of the body of the 

 host, remaining enveloped, however, by a delicate 

 membrane which grows in with it from the wall of 

 the gill chamber. The body is distorted in an extra- 

 ordinary fashion, so that at first sight it seems 

 impossible to trace any resemblance to the form of 

 a typical Isopod. 



Among the Amphipoda there are a few species be- 

 longing to various families of the Gammaridea which 



