MUSCLE ATTACHMENTS AND EPIDERM IN CRAYFISH 387 



away from muscle attachments may contain a great many hori- 

 zontal fibers, some of which pass downwards to join the basal 

 bundle of fibers (fig. 4). Others unite with vertical and oblique 

 fibers which results in the formation of a network within the 

 syncytium. 



Supporting fibrils in the hypodermis are mentioned by Henne- 

 guy, Maziarki, Labbe and Emmel, Maziarki and Labbe believing 

 that they correspond to M. Heidenhain's ' Tonofibrillen ' which 

 are formed in many epithelial cells. In insects Lecaillon could 

 see no other fibers in the epidermal epithelium but the tendon 

 fibers which are continuous with the muscle fibrils. McMurrich 

 found supporting fibrils passing up into the epithelial cells of the 

 mid-gut of terrestrial Isopods from thickenings of the basement 

 membrane. 



In the crayfish the supporting fibrils of the hypodermis show 

 a tendency to collect in the basal portion of the syncytium to 

 form a horizontal layer of fibers which, when composed of many 

 fibers not clearly differentiated by good technique, may have the 

 appearance of a basement membrane. However, a good haema- 

 toxylin stain will show exactly what this 'basement membrane' 

 is. Figures 1, 2 and 4 show clearly that most of the supporting 

 fibrils of the hypodermis eventually reach the basal portion of 

 the syncytium where they take a horizontal course. In some 

 regions (fig. 1) the horizontal fibers form a dense bundle at the 

 inner margin of the syncytium and therby produce a definite limit- 

 ing structure between the hypodermis and the underlying tissues, 

 but in other cases (fig. 2) the basal fibers are not so closely asso- 

 ciated with one another as to form a fibrous membrane. Figure 

 4 shows that the basal fibers may be widely separated from one 

 another and that they may occupy the entire cell-territory between 

 the lower level of the nucleus and inner margin of the syncytium. 

 The same section (left-hand portion of figure 4) shows also that 

 there may be about as many horizontal fibers above the nuclei 

 as below them. In still other regions of the hypodermis horizontal 

 fibers are entirely absent and there is absolutely no limiting struc- 

 ture of any kind between the hypodermal syncytium and the 

 underlying connective tissue. In such places it is impossible to 



