ABT. 5. 2q-0RTH AMERICAN PARASITIC COPEPODS WILSON. 13 



in an invagination of the skin. These setae are solid, but the warts 

 are partially hollow, and to them slender cords of granular proto- 

 plasm lead through the skin. The third group includes the hairs 

 which appear in various places on the skin and the setae that are 

 found on the appendages. These are solid, they arise directly from 

 the surface of the skin and not from a wart or process, and they are 

 not connected in any way with the interior of the body through the 

 skin. 



Under the skin is found a layer of tissue which has been called by 

 Hartmann the chitinogen layer and by Heider the matrix, and which 

 varies considerably in the different genera. In Lemanthropus Heider 

 has described this as not a continuous cellular layer, but instead a 

 protoplasmic ground substance without any distinction of cells, but 

 with small nuclei and granules scattered through it, giving it a 

 granular appearance. In Dichelesthium the chitinogen layer varies 

 greatly in thickness, being reduced to a membrane at and near the 

 joints between the body segments, but increased many times in the 

 center of the segments. Here also the cells are not separated by 

 walls or membranes, but the nuclei are scattered through a common 

 ground substance. There is, however, on the side next to the skin 

 a row of nuclei, slightly larger than the others and placed very close 

 together, which stand out with especial distinctness and have every 

 appearance of a pavement epithelium whose tiny component cells 

 have been completely fused. At the joints the chitinogen layer is 

 made up of this pavement epithelium alone, but elsewhere the ground 

 substance is greatly thickened and gathered into rounded masses of 

 varying size, through which nuclei are scattered indiscriminately 

 (fig. 105). In Nemesis the skin itself is very distinctly striated 

 transversely and the matrix beneath it is so thin that in many places 

 it can only be distinguished with difficulty. It is thicker on the 

 ventral than on the dorsal surface and enters the large basal joints 

 of the swimming legs, but even here no nuclei or cell walls can be 

 seen. 



Inside the matrix is the connective tissue which surrounds all the 

 organs and holds them in place like a mesentery. It is made up of 

 a delicate network of fibers, which are usually branched where they 

 are attached to the inner surface of the matrix. In among the fibers 

 may be seen here and there small connective tissue cells with a dis- 

 tinct nucleus. This tissue enters the large basal joints of the swim- 

 ming legs in Nemesis^ and the modified laminae of the third and 

 fourth legs in Lemanthro'pus^ filling the entire cavity, except for the 

 meshes between the fibers of the tissue itself and the portion already 

 filled by the matrix. In the laminate legs of Lernanthropus the 

 matrix is so thin that the connective tissue fibers penetrate through 



3136— 22— Proc.N.M,Vol.60 9 



