332 ME. A. T. JENNINGS ON THE STEUCTFEE OF 



inner side of the mandibles and run forward parallel to these, to 

 end in the grooves on the labium mentioned above. 



(5) The second maxillcd are small obloag plates rising from 

 a short basal joint just internal to the first maxillae. Their inner 

 margins are slightly curved, and they terminate in front in a 

 straight transverse fringed border behind the labial lobes. 



(6) The maxillipedes are considerably larger, and have a wide, 

 well-calcified base articulating somewhat obliquely with the 

 sternal area. The main lobe is quadrate in shape, and has a 

 thickened anterior border lying just behind the fringed margin 

 of the second maxillae. There is a short palp-like two-jointed 

 lobe lying along its inner margin. 



These four pairs of appendages are again covered ventrally, as 

 far forward as the labium, by the first pair of oostegites. 



Taken as a whole the mouth-parts are not strongly developed ; 

 they are comparatively feeble aud soft, with little chitinous or 

 calcareous material, indicating a suctorial rather than a masti- 

 catory habit. The mouth-aperture itself is very small and far 

 forward, and the various appendages converge toward it. The 

 pointed tips of the mandibles would be just strong enough to 

 attack soft tissues, and to keep open a passage through which 

 fluid nutriment could be ingested by the sucking action of the 

 labium and succeeding parts. 



In the case of such Isopods as live on the gills of fish, food 

 may be obtained by such a direct or true parasitism, but a set of 

 jaws like those of OurozeuTctes would probably be capable of 

 dealing also with small organisms if the animal were in a free 

 stage or only holding on by its hooked limbs to the outside of 

 a fish. 



With regard to the grooves in the labium in which the 

 maxillary rods terminate. Professor Howes has kindly called my 

 attention to the fact that in the common Crayfish the endopo- 

 dite of the second maxilla runs across the labium and fits into a 

 depression in the mandibles *. 



II. The Thoracic Region and its Appendages. 



The thoracic region consists of the typical seven segments 

 with wide terga and well-developed epimera. The latter carry 

 the corresponding limb-sockets, and are also prolonged down 



* Cf. Huxley and Martin's ' Elementary Biology,' ed. 1888, pp. 199, 200. 



