286 Changes in the Muscle Cell of Necturus 



of the University of Chicago, he must also express his thanks for valuable 

 suggestions and criticisms. 



DETAILED DESCRIPTION OF SUCCESSIVE STAGES OP DEVELOPMENT. 



The striated voluntary muscle cell of Necturus has been selected on 

 account of the large size of its structural elements, and because a prelim- 

 inary study of my own series of embryological stages, together with those 

 in the Harvard Embryological Collection, assured me that a detailed 

 study would yield new facts. 



The material used was fixed in Flemming's stronger fluid, Zenker's 

 fluid, corrosive-acetic acid, and picro-acetic acid. The nuclear stains 

 employed were Delaficld's liematoxylin, Heidonhain's iron-alum hema- 

 toxylin, alum cochineal and safranin. The cytoplasmic stains were 

 eosine, orange G, and Lyons blue. 



In comparing the various phases of cytomorphosis the cells have been 

 studied in the same relative localities, as often as possible from the fifth or 

 sixth post-aural segment. In comparing the nuclei the so-called resting 

 stages have been selected. It should be stated here that the nuclei, up 

 to the 26-mm. larva, divide by the typical indirect method. This state- 

 ment must be qualified by the fact that thus far centrosomes have not 

 been observed in striated voluntary muscle cells. i\.s to the method of 

 nuclear division in the later and adult fibres, little is known. Macal- 

 lum, 87, 462," states' that among the many hundreds of muscle nuclei 

 which he examined, but a single case of division was observed and this 

 one was found in heart muscle. I have likewise examined many nuclei 

 witli the hope of settling this point, but am as yet unable to say whether 

 the division is direct or indirect. 



When the myoblasts can first be distinguished by their cylindrical 

 outlines, they are heavily laden with yolk granules (Fig. 1, ij) , which 

 vary widely in size, but are quite uniformly distributed throughout the 

 body of the myoblasts. At this time one often finds, in carefully teased ma- 

 terial, cytoplasmic strands connecting the ends of myoblasts in adjoining 

 myotomes (Plate I, Fig. 5, c. s.). These strands are numerous and indi- 

 cate a widely extending syncytium. 



Necturus 6-7 mm. — The anterior myotomes, which are now well de- 

 fined, measure about 0.3 mm. in length. The axial portion or muscle 



- The numbers indicate the year of publication and the page of the citation. 

 No attempt has been made to give a complete bibliography, only those papers 

 teing listed which are not included in the extensive bibliography given by 

 Heidenhain. gs. 



