MONOGRAPH OF THE EXISTING CRINOIDS. 337 



found smooth longitudinally striped fibers and double diagonal striped fibers 

 mixed. The double diagonal striping he interpreted as a contraction phenomenon, 

 for on arm sections in which the fibers were stretched he found only fibers uni- 

 formly longitudinally striped, while on sections of arms very strongly flexed ven- 

 trally he found almost exclusively fibers with a strong diagonal striping, those 

 most flexed having the fibers with the closest spirals. In contrast to Bosshard, 

 Reichensperger was never able to find the smooth type of fiber. 



Keichensperger states that the anisoti-opic substance of the fibers (composing 

 the dark lines) forms only a single spiral system ; the appearance of a crowded 

 double diagonal striping is due to the striping on both sides of the fiber being 

 visible at the same time. The dark stripes appear to be present only in the outer- 

 most layer of the muscle fibers. 



Apart from the spiral bands the muscle fibers in longitudinal section appear 

 homogeneous, without a cortical layer or similar structure. 



In a cross section through a muscle fiber, which gives a circular or more or 

 less elliptical figure, numerous muscle ribs are seen, which appear as more or 

 less elongate wedge-shaped or triangular areas with the smaller ends or apices 

 directed toward the center. The number of these ridges is seldom very high, 

 mostly under 20, and never exceeding 25. They are embedded in sarcoplasma 

 and are separated by moderately large spaces. If the muscle is relaxed the central 

 clear space is moderately extensive; in contraction the form of the individual ribs 

 becomes markedly triangular, and they elongate inward so that the central spaqe 

 becomes small, and in a state of especially strong contraction almost disappears. 



The ribs consist of a matrix in which the myofibrillae lie embedded, mostly 

 in two, rarely in three rows, in general along the edges, the median portion remain- 

 ing free. 



Bosshard describes the nucleus of the the muscle fiber as situated on the side, 

 externally, and as being long and elliptical, commonly surrounded by a somewhat 

 lighter granular zone over which the sarcolemma, not always easily visible, extends. 

 The sarcolemma is often somewhat raised in the region of the nucleus, while over 

 the remainder of the fiber it clings closely to the contractile substance. 



Hamann believes that not one but several nuclei belong to each fiber. He 

 describes them as elongate-oval in form and as lying at approximately equal 

 intervals on the outer surface. He says that in Ilellomefra glaciolis these nuclei 

 are very large; in Antedon mediterranea they are slimmer and smaller; in the 

 latter the longest fibers in a state of weak contraction are 0.5 mm., the nuclei being 

 0.04 mm. in length. 



Reichensperger says that the single nucleus occupies a position on the border 

 of the clear central area within the fiber. 



On the insertions of the fibers compact plates are developed in which no 

 details can be made out. These adapt themselves to the contour of the meshes 

 in which lie the skeletal parts. From the more intensive staining of these plates 

 and of the adjacent ligamentous portion of the fibers it appears almost as if a 

 special substance was secreted to form the attachment. 



