MUSCLE. 131 



embryos j but the deficiency in my researches may be sup- 

 plied from the description given by Valentin (Entwicklimgs- 

 Geschichte, p. 268), from which the following passage is 

 extracted : " Long before separate muscular fibres can be dis- 

 cerned, the globules of the primitive mass are seen, arranged 

 in parallel lines, particularly when they arc lightly pressed be- 

 tween two pieces of glass. The granules then appear to be 

 drawn somewhat nearer together, to become completely 

 coalesced, in some situations, while at others the blending 

 takes place only on the one or the other side, and to be com- 

 bined into one transparent mass. In this way filaments arc 

 formed, which, in some situations, have an appearance like 

 strings of pearls, at others, on the contrary, are less sharply 

 indented ; they often also continue slightly puckered on one 

 side, whilst the margin of the other has already become more 

 straight. At a subsequent period, all trace of granules or 

 division in the filament vanishes, and its outline becomes sym- 

 metrically transparent and cylindrical. The muscular fibre 

 usually undergoes no other change until the sixth month, ex- 

 cept that its substance becomes somewhat darker and its 

 cohesion closer. The first traces of transverse striae are ex- 

 hibited in the sixth month. These fibres are the primitive 

 fasciculi of muscle and not the primitive fibrils, which latter 

 are formed by a splitting of the fasciculus into smaller fibres. 

 From the period at which the muscular filaments become 

 transparent and uniform, masses of globules, of a more or less 

 spherical form and somewhat larger than the blood-corpuscles, 

 begin to accumulate between them. They diminish again 

 afterwards, and, blending with the gelatiniform mass which 

 connects them, become converted into the connecting areolar 

 tissue." 



The youngest embryos in which I have investigated the 

 generation of muscle were those of the pig, measuring three 

 and a half inches in length. If a portion of one of the super- 

 ficial dorsal muscles be removed from an embryo pig of that 

 size, and examined under the microscope upon a black ground, 

 a transparent gelatiniform mass is observed, in which parallel 

 fibres (primitive fasciculi of muscle) run in close contact, 

 having- a whiter appearance than the surrounding gelatinous 

 substance. As development proceeds, the transparent sub- 



