12 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 60 



Integument. — In none of the genera is the skin hardened into 

 inflexible chitin, as occurs in so many of the Lernaeidae. The modi- 

 fications of the skin, called variously carapace, dorsal, or lateral 

 plates, wings, lobes, etc., are often hardened into chitin, as in Antho- 

 soma^ Nemesis., and DichelestMum.^ but there are also some genera in 

 which they remain soft, as in Lernanthropus and Bassettithia; but 

 in sections that are double-stained the skin always takes the red 

 eosin, but refuses the second color, showing that it has been modi- 

 fied even though it remains soft. Such a section demonstrates that 

 the skin is made up of very thin layers packed closely together. 

 Moreover, it is not uniform in thickness, but varies greatly in differ- 

 ent parts of the body. It is nearly always thicker upon the ap- 

 pendages than upon the body itself, and the framework which sup- 

 ports the various appendages, together with the rods and bands 

 which connect the bases of each pair of appendages across the 

 median line, and the framework around the sex openings appear 

 to be formed by a thickening of the skin. A comparison of the dif- 

 ferent layers of the skin shows that the outer layers are denser and 

 more homogeneous in structure, darker in color, and more strongly 

 refractive than the inner layers. Consequently Heider was led to 

 the conclusion that the increase in thickness takes place by the 

 addition of layers from the inside, which seems probable. Another 

 notable difference in thickened portions of the skin is that the inner 

 layers often show a distinct granulation and sometimes an irregular 

 striping, perpendicular to the surface. Through this skin open ex- 

 cretory ducts leading from the inner chitinogen layer. So far as 

 observed these appear to be usually cylindrical and uniform in diam- 

 eter, rather than funnel shaped as in the Lernaeidae. They are scat- 

 tered everywhere over the skin in great numbers, but are especially 

 numerous upon the head and the free edges of the carapace and 

 dorsal plates. But beside these slender ducts there are a few along 

 the edge of the dorsal carapace, which are funnel shaped and whose 

 diameter is much larger. And the inner or larger end of the funnel 

 is oval rather than circular in outline. A pair of large ducts open 

 between the bases of the maxillipeds and a similar pair on either side 

 near the bases of the first and second antennae. 



The outgrowths of the skin are of three kinds. First, there are 

 processes of the skin itself, soft in texture, hollow, and filled with the 

 chitinogen layer from the inside of the body. These are found in 

 considerable numbers on the antennae, especially on the terminal 

 joints, and may be designated as tactile processes. Here also belong 

 the large setae on the anal laminae, which are hollow and whose 

 lumen is filled with tissue from the inside of the body. A second 

 group comprises the tactile setae which arise from small warts placed 



