54S DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



muscle cases, is nearly constant throughout the whole vertebrate 

 series. Both extremities of the prism are covered by a thin 

 layer of fluid (muscle-case fluid). Between each two muscle 

 cases is a basal membrane, by which the cases are separated 

 from one enother. Each case, however, only possesses a single 

 lateral membrane, investing it annularly, which fuses with the 

 two terminal basal membranes. The muscle cases are arranged 

 in the form of regular disks in the transverse direction of the 

 spindles, which may be called muscular fibres. Each muscle 

 compartment consists of a basal membrane, which appears in 

 profile as a transverse line. Then in the longitudinal view of 

 the muscle spindles there follows one half of a clear transverse 

 band, a dark transverse band, then the half of the succeeding 

 clear transverse band, then again the transverse line formed 

 by the septum, and so on. 



The most noticeable difference in the signification which 

 Hensen on the one hand, and Krause on the other, give to the 

 appearances presented, is that Krause regards that as a muscle 

 prism, and consequently as an anisotropal part, which Hensen 

 holds to be intermediate substance, and an isotropal part. 



Heppner* has raised objections to the accounts given by 

 Hensen and Krause. In his opinion, the refractile zone (muscle- 

 case fluid of Krause, transverse disk of Hensen) is only the 

 expression of total reflexion which occurs at the line of de- 

 marcation between the chief and the intermediate substance. 

 In support of his views he adduces the circumstance that the 

 position of the refractile band, in relation to the limiting layer 

 dividing it (median disk, Hensen transverse line, Krause), can 

 be altered by changing the position of the mirror, and that in 

 certain positions of the mirror the bands may disappear al- 

 together. He adduces also the appearances presented under 

 polarised light. If the visual field be coloured by a Nicol's 

 prism, both the refractile band and the dull disks constantly 

 appear to be of the same colour. Both Hensen and Krause, 

 however, maintain that only one of the two is anisotropal. 



So far as regards the explanation given by Krause and 

 Hensen of the appearances first described by them, I must 



* Max Schultze's Archiv, Band v. 



