298 ZOOLOGY 
They are dioecious and markedly dimorphic, the dwarf male 
living attached to the body of the female. The female is 
somewhat disk-shaped, asymmetrical, and with but slight 
traces of segmentation, and no eyes. The male is elongated, 
segmented, and provided with eyes. The mouth parts are 
rudimentary ; in the female the seven thoracic legs bear 
oostegites, which form a brood-pouch. In those species with 
a piercing mouth the upper and lower lps form a suctorial 
tube, within which the mouth parts are enclosed in the form 
of piercing stylets. A very remarkable fact connected with 
the parasitism of the Bopyridae is that the presence of certain 
species of this group has the effect of materially altering the 
reproductive organs of its male host. For instance, a male 
Pagurus infested by Phryxus paguri has its abdominal append- 
ages of the female type, and its testis is degenerate and the 
spermatozoa imperfect. The same is true for many other 
species, 
In the family ENTonIscipAE the more complete parasitism 
has involved a greater departure from the ordinary Isopod 
type. Their body is a limbless sack, which lives in an in- 
vagination pushed into the bodies of Cirrhipedes, Paguridae, and 
Crabs. The invagination retains its opening to the exterior. 
The sexual forms of Portunion are very remarkable; the 
large deformed parasite is a protandrous hermaphrodite, 
functioning in its adult stage as a female; besides this form 
there are small males which remain in a larval stage, and also 
degraded complemental males. It seems that out of the 
numerous larvae, those which obtain the most advantageous 
position in the host will become the hermaphrodites and will 
ultimately produce eggs; those which occupy the next best 
position become the males, which retain their larval features, 
whilst the most disadvantageously situated larvae degenerate 
and form the complemental males. The genus Cryptoniscus is 
commonly parasitic on the Rhizocephala, which are themselves 
parasitic on other Crustacea; it is stated that if the Rhizo- 
cephala die the Isopods still continue to receive nutriment 
through the root-like processes of their dead hosts, as if they 
were parts of its own body. 
The family ONIScIDAE, the wood-lice, have become terres- 
