THE JSOPODA 



197 



Lund, and Hansen. The remarkable group of the Epicaridea has 

 attracted many investigators, but it is especially to the memoirs of 

 Giard and Bonnier that the student must turn for a clear account 

 of their structure and complicated life- 

 histories. As regards the internal anatomy 

 of the Isopoda, the literature is scattered 

 and fragmentary, but Delage's study of 

 the circulatory system must not be passed 

 without mention. Bullar's discovery of 

 hermaphroditism among the Cymothoidae 

 is also noteworthy. 



MORPHOLOGY. 



In the majority of the free -living 

 Isopoda the body (Fig. 118) is more or 

 less flattened, with an oval outline as seen 

 from above and with a short abdominal 

 region. In the Arcturidae and Anthuridae, 

 however, it is elongated and subcylindrical, 

 and in some of the latter family it is almost vermiform. In Phrea- 

 toicus (Fig. 119) the body is laterally compressed and the aspect is 

 that of an Amphipod. In the parasitic Epicaridea the adult female 



Fio. 118. 



scuber, 9, doisal view, 

 x 3. (After Sars.) 



FIG. 110. 

 1'hrcatoicns usslmilis, 9 , from the side, x S. (After Chilton.) 



becomes more or less distorted and deformed and may even lose all 

 trace of segmentation. In addition to the first, the second thoracic 

 somite becomes united with the head in the Gnathiidae and Serolidae, 

 in the genus Stenasellus among the Asellota, and in a few Valvifera. 

 The last thoracic somite occasionally remains of small size and 

 without appendages in the adult, as it nearly always is in the 



