216 E. A. Schäfer, 



Unquestionably the lamellar muscle-column is thus subdivisible. 

 The fact that it so readily splits up in alcohol preparations into the 

 fine longitudinal elements which are usually termed fibrils, is a suffi- 

 cient proof of this. But an indication of the subdivision can also be 

 seen in transverse sections of the gold-acid muscles. If a well-stained 

 separated disk be carefully examined with the highest powers, parti- 

 cularly if it happen to have been somewhat compressed so as to open 

 out the radiating lines of the transverse networks, there can frequently 

 be obtained evidence of the existence of delicate septa which pass 

 obliquely across the section of the lamellar muscle-column (Figs. 19, 20) 

 and indicate that it is really itself formed of smaller angular columns, 

 which correspond pretty nearly in point of size with the polygonal 

 columns which are met with in muscles of other insects (Fig. 15). 

 The difficulty of detecting these septa arises from the fact that the 

 radiating filaments of the transverse networks tend, by their distinct- 

 ness and the manner in which they refract the light, to obscure any 

 structure in the muscular substance between them, and as the com- 

 paratively coarse network-filaments do not extend across the lamellae 

 into the subdividing septa, these septa remain under ordinary circum- 

 stances invisible. When, however, by compression the filaments are 

 more separated the septa can be seen. But in the leg-muscles of some 

 insects which have radiating and lamellar muscle-columns, oblique septa 

 may be seen crossing the lamellae in transverse section even without 

 the aid of artificial means of separating the principal lines of the 

 network, and in these the subdivision of the lamellae is very obvious. 

 Such fibres, which are represented by various authors, afford a distinct 

 transition to those in which the section of the muscle columns is 

 polyhedral and the transverse networks are uniformly arranged over 

 the Avhole surfaces of the muscle-disks (Fig. 15). 



We thus arrive at the conclusion that the lamellar plates of 

 those fibres which have a radiating section are compounded of smaller 

 angular columns or sarcostyles which are equivalent to the pris- 

 matic sarcostyles of fibres which have a reticular section. We have 

 yet to consider the evidence as to the fibrillation of these sar- 

 costyles. 



