392 HAL DOWNEY 



of some vertebrates, Goronowitsch having shown that in birds 

 the musculature of the visceral arches is derived from cells of the 

 neural crest and from the outer ectoderm. Julia Piatt does not 

 admit the development of muscles from wandering extoderm cells 

 in Necturus, but she does claim that the branchial cartilages and 

 the anterior portions of the trabecular bars are developed from 

 ectoderm, while Goronowitsch claims that in birds a portion of 

 the mesenchyme, cutis and skull in the region of the midbrain 

 are formed from ectoderm. According to Kastschenko the mesen- 

 chyme is derived from all three germ layers, from cells which 

 are not used up in the formation of epithelial structures, and 

 v. Kupffer derives the branchial cartilages of Petromyzon from 

 the deeper layers of the ectoderm. 



Facts like these show that we must be careful in our state- 

 ments regarding the origin of various structures from certain germ 

 layers until we have exact ontogenetic studies of those structures, 

 and this is especially true of the invertebrates. 



The peculiar arrangement which provides for union between 

 muscle and tendon fibrils in the crayfish suggests independent 

 origin and secondary fusion of those structures, but the ontogene- 

 tic proofs for this are lacking. In any case, the method of union 

 between the two types of fibrils remains quite different from what 

 it is in vertebrates. In the latter there is direct continuity between 

 muscle and tendon fibrils, as has been recently proven by Oskar 

 Schultze 1 for man and several groups of vertebrates. His results 

 have been confirmed by other investigators (see Schultze's Leipzig 

 paper for further literature on the subject), and the writer can 

 testify that his preparations show all that is claimed for them. 

 That many authors believe that the same conditions obtain .in 

 Arthropods has already been pointed out. However, the present 

 investigation does not warrant this conclusion for the crayfish. 

 Here the ends of the muscle fibrils are surrounded by fine branches 

 of the tendon fibrils, some of which may pass in between the muscle 

 fibrils for a considerable distance. 



1 Verhdl. der Phys.-Med. Gesellsch. zu Wurzburg N. F. Bd. 41 and Verhdl. 

 der Anat. Gesellsch, 25. Vers., Leipzig, 1911. 



