362 



HISTOLOGY 



not been especially worked out in the earthworm. Also the renewal 

 processes which must take place to repair the loss by attrition in this 

 hard-burrowing animal are not understood. For methods of cuticle 

 renewal, see the following description of this process in the Crustacea. 

 The two have, doubtless, much that is similar. 



The lobster is also an animal that has an epithelial layer of cells on 

 the outside of its body and a cuticle covering these cells. The columnar 



cells composing this epithe- 

 lium are large and well 

 formed, and vary much as 

 to length and the .develop- 

 ment of their characteristic 

 organs, which are the same, 

 however, and easily distin- 

 guished wherever seen. The 

 supporting fibrils are partic- 

 ularly well seen, and are 

 very instructive because of 

 the fact that they are to be 

 divided into two groups ac- 

 cording to whether muscles 

 are attached to the cells to 

 which they belong or not. 

 In Figure 328 a portion of 

 the epithelium of a lobster 

 is represented with the 

 cuticle lying on its upper 

 surface and two kinds of 

 supporting fibrils repre- 

 sented in the cells. The 

 cells on the left are from 

 a region where the fibers 

 of a muscle are attached, 

 and the fibrils of this mus- 

 cle can be seen so closely 



FIG. 32 8. -Portion of the new integument of a lobster, Connected with the fibrils 

 Homarus. conn.t.nu., connective- tissue nucleus; bl.c., of the epithelial Cell that 



they seem to be direct con- 

 tinuations of them. The supporting fibrils are, in this case, made 

 strong and straight so that they can bear the strain of the contraction of 

 the muscle. In the adjoining half of the epithelium, in the right of the 

 illustration, it can be distinctly seen that the supporting fibrils of the cells 

 are not called on to withstand any such strain because of the blood space 



mus. c. 



