558 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 55. 



former of which is fringed at the tip, and the two are joined so as to 

 leave an opening on either side. The mandibles are inside the tube 

 and are stylet-shaped, their adjacent surfaces set with a row of fine 

 teeth. 



The first maxillae are on the outside of the tube; each is one-jointed 

 and tipped with a tiny spine. The second maxillae are on the ventral 

 surface of the head behind the mouth tube ; each consists of a simple 

 finger-like joint, projecting ventrally and tipped with a small claw. 



The maxillipeds are considerably larger, and each consists of a 

 basal joint fused with its mate across the midline and a free terminal 

 joint tipped with a stout claw. As growth progresses and the vari- 

 ous processes grow out upon the cephalothorax some of these ap- 

 pendages usually disappear, or they may be changed somewhat in 

 position, so that in the mature adult they are hard to find. But 

 careful search will usually reveal at least some of them. The swim- 

 ming legs are very quickly broken off and are never found upon the 

 adults of either sex. But on the same young female whose mouth 

 parts are shown in figure 12 there were the remains of the first and 

 fourth pairs. The first pair were on the cephalothorax and the 

 fourth pair on the anterior end of the trunk. We can judge where 

 tli« others must have been by the breaks in the longitudinal muscu- 

 lature. 



INTERNAL MORPHOLOGY. 



Body vjall. — The body wall is similar to that of the Lernaeidae, 

 being made up of two layers, an outside transparent layer, which in 

 this family never becomes chitinous except in the neck and horns, and 

 an inner opaque layer, made up of cells containing nuclei. 



The outer layer is quite thin over the cephalothorax and trunk in 

 Paeon, but is conspicuously thickened in the neck and at the pos- 

 terior corners of the genital segment; in Sphyrion and Rebelula it 

 is thick and leathery all over the body. It is made up of thin lamel- 

 lae packed closely together without intervening spaces, and contains 

 pore canals connected with the inner layer. The latter varies in 

 thickness in different parts of the body, but nowhere attains any- 

 thing like the depth found in some of the Lernaeidae. Nor does it 

 anywhere form glands like those seen in Sarcotretes and other Ler- 

 naeids. But it does make up a spongy tissue which fills the cephalo- 

 thoracic and posterior processes, as well as those portions of the 

 cavity of the head and trunk not otherwise occupied. In bulk, there- 

 fore, it is by far the most extensive tissue in the body. 



Muscular system of the female. — We know nothing of the muscula- 

 ture of the free swimming lan^a, but it must of necessity be more 

 extensive and Complicated than that of the adult. The youngest 

 of the developmental stages of Sfhyrion here mentioned shows the 

 same muscles as the matured adult with one exception. There is in 



