MUSCLE ATTACHMENTS AND EPIDERM IN CRAYFISH 385 



eluded from his studies on the development of the crayfish that 

 the tendon fibrils are formed from the ectoderm, but that the 

 muscles are developed from mesoderm. Emmel has shown that 

 in the regenerating lobster claw the muscles and hypodermis are 

 developed from an ectodermal syncytium. The tendon fibrils 

 are the non-striated ends of the muscle fibrils. The basement 

 membrane which is formed at first is also a product of the ecto- 

 dermal syncytium. 



The above gleanings from the literature show that the problem 

 of muscle attachment in Arthropods can hardly be regarded as 

 settled. We find a variety of opinions even on such a question 

 as the exact mode of attachment of the muscle fibrils to the tendon 

 fibrils, the solution of which depends chiefly on good technique 

 and careful observation of sections of adult tissue. It seems, 

 therefore, that any new observations in this field may be of value. 



The following account of muscle attachment in the crayfish is 

 based on a study of material from the histological collection of 

 the department of Animal Biology of the University of Minnesota. 

 The sections were made through the region of muscle attachment 

 in the claw of a crayfish after the chitin had been stripped off. 

 The fixation of the material is good. The sections are stained in 

 a haematoxylin combination. which gives a splendid differentia- 

 tion of the finer cell structures. 



The epiderm or hypodermis, as it is usually termed by entomolo- 

 gists, of the large claw of the crayfish may consist of one (figs. 

 4 and 5) or several (fig. 1) layers of extremely irregular cells 

 which are so closely associated with one another that it is usually 

 quite impossible to distinguish cell boundaries. A study of sections 

 through regions located between the points of muscle attachment 

 (figs. 1, 2, 4) shows very clearly that there are no cell boundaries, 

 and that the hypodermal layer is composed of a protoplasmic 

 syncytium in which the nuclei have a very irregular distribu- 

 tion, a condition which was described by Henneguy for various 

 Arthropods and by Emmel in the regenerating claw of lobster. 

 In some regions (fig. 1) the presence of small and large irreg- 

 ular spaces gives the syncytium the appearance of an extremely 

 irregular protoplasmic network the strands of which are extremely 



