78 0. F. MARSHALL. 



In a later paper Engelmann 1 states that the contractility of 

 the muscle-fibre is always connected with fibrillar elements in 

 the fibre ; and he compares these with fibrillar elements in the 

 protoplasm of some of the Rhizopods and Infusoria, &c. 



Retzius 2 describes very carefully a network in the muscle- 

 fibre of Dytiscus and other forms. This network consisted of 

 (i) transverse networks placed at regular intervals, and corre- 

 sponding in position to Krause's membranes, (ii) Longitu- 

 dinal bars parallel to each other, and apparently running the 

 whole length of the muscle-fibre, and connected with the 

 transverse networks. His results were obtained partly by 

 transverse and longitudinal sections, and partly by teased 

 preparations. He also employed the following method of 

 gold staining : the specimens were placed for twenty-five 

 minutes in ^ — \ per cent, gold chloride, either with or without 

 previous immersion in 1 per cent, formic acid ; then in 1 per 

 cent, formic acid for ten to twenty hours, and exposed to the 

 light. He gives the following description of the muscle-fibre 

 of Dytiscus : In the axis of the fibre there are one or more 

 rows of muscle-corpuscles, the protoplasm of which is produced 

 into several (2 — 5) processes from which finer processes arise 

 forming the transverse networks. Each muscle-corpuscle 

 is in connection with five or six successive transverse net- 

 works. The longitudinal bars of the network he describes 

 rather doubtfully as consisting of rows of dots (p. 8), but he 

 describes and figures them projecting freely in some prepara- 

 tions. The matrix is structureless, and is only slightly 

 stained by the gold. The sarcolemma is apparently closely 

 attached to, but probably independent of, the network. The 

 nerve endings appear to be in close connection with the 

 transverse networks. The function of the network he was 

 unable to determine, but states that it is probably not merely 

 a supporting framework, but actively concerned in contraction. 

 He does not, however, regard it as the true contractile part, 



1 'Pfliiger's Arckiv,' Bd. xxv, 1881, pp. 538—565. 



2 " Zur Kentniss der quergestreiften Muskelfaser," ' Biologische Unter- 

 suchungen,' 1881, pp. 1 — 26, Pis. i, ii. 



