MUSCLE ATTACHMENTS AND EPIDERM IN CRAYFISH 393 



Coagulated blood plasma is found in some of the spaces of the 

 hypodermal syncytium and in occasional spaces which occur in 

 the layer of horizontal fibers at the base of the epiderm. This 

 indicates that the vascular circulation is in very close relation 

 with the hypodermis. 



SUMMARY 



The hypodermis of the crayfish consists of a protoplasmic syncy- 

 tium containing one or more layers of nuclei which have a very 

 irregular distribution within the syncytium. 



Supporting fibers and fibrils are found everywhere within the 

 syncytium. In some regions they all take about the same course 

 and eventually reach the basal portion of the syncytium where 

 they run in a horizontal direction. 



The basal layer of fibers shows great variation in the number 

 of fibers entering into its composition and in their proximity to 

 each other. In some cases the basal fibers occupy the entire 

 territory between the nuclei and the lower border of the syncytium, 

 and in others this layer is absent altogether. On account of these 

 variations this layer of fibers can not be classified as a true base- 

 ment or intermediate membrane. 



Fibers from the supporting tissue are continuous with those of 

 the hypoderm and some of them join the basal layer of hypodermal 

 fibers which, in the regions of muscle attachment, usually pass 

 between the ends of the muscle fibrils and the tendon fibers by 

 means of which the muscles are attached to the chitinous exoskele- 

 ton. 



The tendon fibers are bundles of fine fibrils, similar to those 

 found in other regions of the epiderm. At their inner ends the 

 tendon fibers are resolved into their constituent fibrils which usu- 

 ally anastomose with neighboring fibrils in such a way as to pro- 

 duce a network at the base of the tendon. Fibers from other 

 regions of the hypoderm and from the supporting tissue frequently 

 join this network (fig. 1). 



Tendon fibrils, and fibrils from the intermediate network or 

 basal layer of hypodermal and supporting tissue fibrils penetrate 



