Albert C. Eycleshymer 291 



Transverse sections show that the bases of the so-called brnshes or 

 cones may take on different forms, as represented in Fig. 11. In this 

 figlire the two myoblasts on the right exhibit the patterns often fonnd, 

 while the three on the left represent forms less frequently seen. The 

 condition pictured in tlie lowest myoblast might lead to the supposition 

 that there is a peripheral band of fibrillge, but in all cases of this kind 

 the study of serial sections shows that the fibrillse converge on the noto- 

 chordal side of the mj^oblast. 



If a transverse section through the end of a given myoblast be com- 

 pared with a like section through its middle, it will be found that the 

 number of fibrillas in the former is greatly in excess of those in the latter. 

 This fact is in harmony with the assumption that the fibrillge increase in 

 number through longitudinal division. 



The nuclei have increased in number until four and often five are 

 found in each myoblast. Transverse sections of this stage show that 

 they no longer occupy an axial position, but are eccentrically placed, 

 often tying close against the outer side of the myoblast, in a position 

 intermediate between that shown in Figs. 11 and 12. The nuclei have 

 a somewhat different outline from those of the early stages, in that they 

 are longer and more pointed, as shown in Plate III, Fig. 27. The 

 nuclear membrane in many nuclei is lined by a layer of karyosomes, 

 which is so closely applied to the membrane as to appear inseparable 

 from it. The meshes of the linin network are larger, with a noticeable 

 increase in the diameter of the threads. The plasmomeres have decreased 

 in number, and in many nuclei have disappeared entirely. 



The karyosomes are in general more numerous and larger than in any 

 of the earlier stages. They are irregularly scattered throughout the 

 nucleus, and vary in form from round to elongated masses with numer- 

 ous processes extending along the linin threads. In some cases they are 

 arranged in two or three irregular rows which extend, in a general way, 

 parallel with the long axis of the nucleus. Frequently there is found a 

 nucleus with a marked axial aggregation of karyosomes, but in the 

 greater number there is a tendency towards a peripheral condensation. 



Nedurvs 21-26 mm. — In the larvge of these lengths the myotomes 

 measure about 0.6 mm. and show a corresponding increase in diameter. 

 The myoblasts are not notably different in general character from those 

 of the preceding stages. 



The peculiar arrangement of the yolk granules observed at this time 

 (Fig. 7) leads me to remark that in the early stages the myoblasts pos- 

 sess an enormous number of large yolk spheres which often equal the 

 nucleus in size. As development proceeds these spheres become broken 



