MONOGRAPH OF THE EXISTING CRINOIDS. 429 



undergo wide differentiation. First, moving out from the innermost portions, 

 ganglion cells appear, though only in relatively small numbers, followed by sup- 

 porting cells, and later, when the tentacles have entirely regenerated, epithelial 

 gland cells are formed. The schizocoele cavity appears rather early. The cilia 

 are rather later in making their appearance. 



Eeichensperger believes that the rebuilding of the epithelial nerve layer for 

 the most part can be traced back to the outgrowth of the original nerves, but that 

 the newly formed ganglion ceils also assist in the reconstruction to some extent. 



Genital cord. The genital cord undergoes extensive degeneration. In in- 

 dividuals not sexually mature it shrivels and disintegrates as far as the branch 

 given off to the preceding pinnule, though in sexually ripe animals the degenera- 

 tion is much less far reaching. In both cases regeneration proceeds in the same 

 way, proceeding exclusively from the unchanged portion and progressing rapidly 

 once it has set in. 



First a bud is formed from the approximate walls of the genital canal and 

 genital tube, to which the genital cord apparently also contributes. This bud 

 penetrates the very loose connective tissue which separates the divisions of the 

 brachial ccelome, and its various elements become reasserted. 



Differentiation of the elements in the genital cord occur very early, numerous 

 cells becoming converted into germ cells. 



Muscles and ligaments. In well-advanced regenerating buds the first indica- 

 tion of the formation of the muscles and ligaments consists in the accumulation of 

 mesenchyme cells in certain definite regions. The muscle cells make their appear- 

 ance somewhat later than those of the dorsal ligament, and at first are only with 

 difficulty distinguishable from the latter. 



The dorsal ligament cells are oval and somewhat elongated, with a finely 

 dotted plasma and a moderately large nucleus, containing usually several large and 

 many small nuclear bodies. They collect at the ends of the ossicles and move 

 toward the dorsal nerve cord, in the immediate vicinity of which the oldest cells 

 are found. 



The cells now elongate, and fine fibers can be made out. Whether these fibers 

 are internal, or whether the cell rests upon them, has not been definitely determined. 

 When the formation of the fiber bundle is completed the cells are entirely 

 different in appearance. The nucleus stains so intensively that no details can be 

 distinguished. The amount of the now homogeneous cytoplasm gradually dimin- 

 ishes until it is present only as a thin clear film about the nucleus. From the cells 

 more and more fine fibrils are produced whicli in the middle lie closely together, 

 but at either end become spread out brush-like and, gradually turning toward each 

 other within the meshwork of the skeletal pieces, finally meet, producing regular 

 bows or loops. These loops lie usually in several or numerous rows, and the 

 farther they are from the middle of the fiber bundle the more isolated are the 

 fibers and the more difficult it becomes to differentiate them. 



Often, especially in the earlier stages, only the fibers of a single bundle join to 

 form a loop, but later the fibers of neighboring bundles become knotted together. 



