Albert C. EyclesJiynier 289 



fibrilla3 do not as 3'et show an}^ indications of transverse bands or mark- 

 ings. 



Necturus S-9 mm. — This stage, which is well illustrated by Fig. 8, 

 shows an extension of the fibrillated tract. The apparent apex of the 

 cone or brush is not far removed from the place at which it was located 

 in the preceding stage. The converging fibrillffi, however, no longer ter- 

 minate here, but continue in a closely aggregated bundle or tract through- 

 out the length of the myoblast, and again spread out into a similar brush 

 or cone at the opposite end. To make the description more complete, it 

 should be remarked that at each end of the myoblast a conical group of 

 fibrillar is formed and these extend from either end towards the middle 

 until they meet and form a continuous tract. Where a considerable num- 

 ber of the fil)rill?e are close together, as represented in Fig. 8, the trans- 

 verse markings are now plainly seen, but as they spread out in small 

 groups or singly, these markings are more obscure and are indicated only 

 in the moniliform outline of the fibril. 



This peculiar arrangement of the fibrilhe, in the myoblasts of Necturus, 

 is similar to that described and figured by Heidenhain in the fibrillation 

 of the ciliated cells in the hepatic ducts of Helix and in the intestinal epi- 

 thelium of the frog, where the fibrillge take on a conical arrangement 

 with their apices on one side of the cell. An almost identical arrange- 

 ment of the fibrillar has been found by Godlewski, 02, in the myoblasts 

 of the rabbit, in which form he states that the fibrillar of one myoblast 

 extend over into the myoblast of an adjoining myotome. This relation 

 I can positively say docs not exist in Necturus. 



Necturus 9-10 mm. — The myotomes in the post-aural region have now 

 reached a length of about O.-t mm. and present the general appearance 

 shown in Plate I, Fig. 2. The clear zones at either end of the myoblast 

 are wider; the fibrillated tracts are considerably increased in diameter, 

 and the notochordal sides of the myoblasts are better defined. In the sec- 

 tions it is not difficult to trace the outlines of the myoblasts from one 

 end of the myotome to the other and to see that now, as in the earlier 

 stages, the ends of the myoblasts in adjoining myotomes are frequently 

 connected by cytoplasmic strands. 



Transverse sections of the myotome at this time show a well-defined 

 cell membrane which in teased preparations is usually ruptured. Since 

 there are as yet no mesenchymal cells, either between the ends of the 

 myotomes or among the myoblasts, this membrane must represent what- 

 ever sarcolemma the myoblast now possesses. 



Necturus 12 mm. — Previous to this time there is no indication of the 



