DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 897 



notochord has increased in diameter, and in transverse section is disproportionately large 

 as compared with the slender character of the trunk in this species. The partitions 

 stain deeply, but present no noteworthy histological features. A Clupeoid, double the 

 length of the example just referred to, shows little alteration in the structure of the 

 notochord. 



During development Balfour states (No. 11, p. 456), " that most of the protoplasm 

 with the nuclei is caused to pass to the periphery, where it forms a special nucleated layer, 

 sometimes divided into special epithelial-like cells " of which he gives a figure in the case 

 of the salmon, " while in the meshes of the reticulum a few nuclei surrounded by a little 

 protoplasm still remain." Ryder mentions that he has not been able to see nuclei in the 

 cells of the notochord ; # but such appear to be present in Anarrhichas, since small gran- 

 ular areas, distinctly stained, occur frequently throughout. They are less definite than 

 the nuclei of the newly-hatched salmon, which form large rounded or ovate bodies with 

 granular contents, and nucleoli in the majority of the cells (PL XXVI. fig. 5). Moreover, 

 the cellular rim within the sheath, as Gegenbaur shows in the salmon,t is well seen in 

 longitudinal vertical section in the wolf-fish, since it separates from the sheath as a deeply 

 stained layer of cells of some thickness. In the post-larval Coitus scorpius (f inch long) 

 a single layer of large nucleated cells lines the chordal sheath, now firm from the deposi- 

 tion of hyaline matter. The central mesh work of chordal cells appears to be diminishing 

 in diameter, and along with the cell-layer just named is separated from the hard sheath. 

 A similar grouping of nucleated cells is very marked within the chordal sheath of T. gur- 

 nardus, £ inch in length ; indeed, there are several features of interest at this stage of 

 post-larval life, for external to the round nucleated cells J just mentioned, with their 

 definite nucleus and clear cell-contents, is a layer of very much flattened cells. The 

 large cellular spaces of the notochord have thin walls irregularly folded, and the more 

 centrally situated chambers are more spacious than those outside. This condition is also 

 well marked in the post-larval wrasse, about ^ an inch in length, the larger cells being 

 central. When ^ of an inch in length the notochord of the post-larval Gadoid shows 

 indications of vertebral divisions, dense transverse aggregations of nucleated tissue, 

 flattened cells, and amorphous notochordal plasma, forming serial rings on the inner sur- 

 face of the chordal sheath. As these ridges grow they rupture the hyaline sheath. 



In the beginning of March the chief change in the notochord of the wolf-fish is the 

 increase in the size of some of the median cells, those next the circumference being 

 smaller. The nuclei, with their nucleoli, are also very distinct in many. Little altera- 

 tion occurs in the general arrangement of the notochordal cells in May (PL XXVI. 

 fig. 4), and though the development of the vertebral elements has made considerable 

 progress, yet the cells show little or no modification of importance on the 20th of June. 



* He writes — " In just hatched embryos of several genera I have as yet failed to discover any trace of nuclei in 

 those portions of their walls which extend into the body of the chorda" (Rep. U. S. Fish. Commiss., 1882, p. 511). 

 t Elements of Comp. Anat., translated by Prof. Jeffrey Bell, p. 427, fig. 221 . 

 % In prepared sections these cells recall precisely the appearance of the early blood-corpuscles in Teleosteans. 



VOL. XXXV. PART III. (NO. 19). 6 Y 



