384 HAL DOWNEY 



muscles. They correspond to M. Heidenhain's ' Tonofibrillen ' 

 which are formed in many epithelial cells, according to Maziarki 

 and Labbe, and Janet observed that they may become chitinous. 

 Lecaillon's observations show that a tendon may divide into two 

 parts and that two tendons may fuse. 



The tendon fibers are developed from the ectodermal epithelium 

 according to Claus, Henneguy,Leydig,Duboscq, Maziarki, Labbe, 

 Janet, Snethlage, Reichenbach, van Rees, Emmel, Riley and 

 Bertkau, but Tullberg and Braun derive them from the connec- 

 tive tissue. Most of those authors who believe that the tendon 

 fibers are prolongations of the muscle fibrils also believe that the 

 muscles are products of the mesoderm, which compels the con- 

 clusion that the tendon fibers are also of mesodermal origin. This 

 view, however, is not shared by Nowikoff and Snethlage, nor by 

 Reed, Ost and Emmel. All of these authors derive the muscles 

 and the epidermis from the ectoderm, the three last named basing 

 their conclusions on a study of regenerating tissue. 



A study of the development of the muscles has been made by 

 Henneguy (insects), Reichenbach (crayfish) and vanRees (insects). 

 The work of these authors shows the muscles to be of mesodermal 

 origin, while the investigations of Snethlage (Artemia salina) fur- 

 nish equally convincing proof for the ectodermal origin of the 

 muscles in normal ontogeny. Reed, Ost and Emmel have shown 

 that the regenerating muscles are of hypodermal origin. Henne- 

 guy studied insect embryos and found that the muscles were 

 developed from mesodermal cells which were in contact with the 

 hypodermis. Epithelial fibrils were differentiated at the same 

 time that the muscle fibrils were formed, and the two became con- 

 tinuous. Snethlage's studies on developing Artemia muscles con- 

 vinced him that they are formed from the ectoderm at the point 

 of insertion. Development from the mesoderm would be impos- 

 sible, because a mesoderm in the sense of a distinct germ layer 

 does not exist in these forms, van Rees worked on the metamor- 

 phosis of Musca vomitoria and found that the basal portions of 

 the hypodermal cells become spun out into fine processes which 

 push the basal membrane away from the epithelial cells. These 

 fine processes become the muscle tendons. Reichenbach con- 



