CLARKE, ON STRIPED MUSCULAR FIBRE. 223 



In the domestic fowl, on the fifth day of incubation, the 

 (so-called) voliintarj^ muscular tissue is of a gelatinous con- 

 sistence, and when examined by means of a sufficient magni- 

 fying-poAYcr is seen to consist of the following three elemen- 

 tary parts : — 1, a granular, semifluid blastema or matrix ; 

 2, free nuclei ; and 3, imcleated fibres. 



1. The granules of the blastema vary considerably in size; 

 the largest (PL XI, fig. 1 a) are but little inferior to the 

 smallest nuclei (6), as if they formed a transition from the one 

 to the other. 



2. The free nuclei (fig. 1 b, c, and fig. 3 a) are thickly 

 crowded together in every part of the tissue, and are either 

 globular, oval, triangular, pyriform, fusiform, or somevv^hat 

 crescentic. Each contains one or a pair of globular nucleoli 

 of variable size, and frequently gives off one or two separate 

 processes from different sides (fig. 3 a). During the develop- 

 ment of the muscular fibres these nuclei multiply by subdi- 

 vision, and undergo considerable alterations in shape. 



3. The nucleated fibres at this period, according to their 

 relative state of development, present a considerable variety 

 of appearance. Some of them (fig. 3 b) are but little more 

 than oval or fusiform nuclei, with elongated processes. 

 Amongst these the smaller kind appear to belong to the 

 tendinous and aponeurotic tissues. The majority, how'ever, 

 which are more fully developed have a proportionately different 

 aspect. 



The process of development may be divided into two 

 stages — 



1. That in which the fibres are formed and isolated from 

 the surrounding substances. 



2. That including the changes which they subsequently 

 undergo to complete their development. 



At the beginning of the first stage, or the formation of 

 fibres, granular processes of variable breadth and length, 

 resulting apparenthj from the condensation or coagulation of 

 the surrounding blastema, extend from the opposite sides or 

 ends of a series of nuclei, until they meet and coalesce to form 

 continuous fibres. In these fibres the nuclei are at variable 

 distances from each other, and the processes which grow from 

 them and coalesce are consequently of variable length. In 

 general, the greater the distance between the nuclei the 

 narrower are the processes which unite them. Sometimes 

 they are ranged at considerable intervals in a straight and 

 single series, the processes growing toward each other until 

 they meet, as at fig. 4a; or they are placed irregularly and 

 sometimes in close apposition, as at fig. 5 a, b, the processes 



