896 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



which correspond to the fin-rays. Numerous brown pigment-corpuscles exist in the 

 intervening membrane. From the curved portion of the notochord the hypurals (about 

 six in number) project backward, besides an opaque mass at the tip of the organ, which 

 may be a rudiment of one, though no cartilage-cells can be made out. The fourth ray is 

 much broader than the others, and has the form of a long bent spatula. On comparing 

 the salmon of this period with Lereboullet's trout at a similar stage,* the following 

 differences appear : — The fifth hypural from the tip is large and broad in the trout, instead 

 of the fourth. The fin-rays in the trout are fibrillar throughout, and have no articula- 

 tions ; whereas in the salmon they are only fibrillar along the terminal third, and have 

 the articulations described above. The development of the trout must therefore be slower, 

 though in Lereboullet's figure the hypurals are well formed ; or perhaps the figure itself 

 is deficient. The condition of the tip of the notochord would seem to show that the stage 

 figured is really earlier. 



The pigment in the tail subsequently increases, as also do the fin-rays, which at this 

 stage amount to twenty-three or twenty-four ; whereas Day gives those of the adult at 

 nineteen. Four vertical lines indicate the articulations of the rays — the first or anterior 

 being most curved. 



The caudal region just described, and that of the wolf-fish, offer several interesting 

 points of contrast, the most noteworthy of which is, perhaps, the great complexity of the 

 circulation in the former on hatching, and the conspicuous curvature of the end of the 

 notochord. Besides, the divergent condition of the hypural elements is striking, the 

 salmon having five or six narrow elongated hypurals along the upward flexure, while the 

 wolf -fish shows only the two broad plates, as in GastrosteusA It is probable that this 

 diminution of the hypurals coincides with a reduction in the number of vertebrae in the 

 curved portion of the notochord, a supposition borne out by appearances in the salmon 

 — for indications of six or seven constrictions are visible in that species in the region of 

 the hypurals, that is below the atrophied terminal process, which is lodged between the 

 fin-rays. On the other hand, only two are seen in the wolf-fish, and though not shown 

 by Huxley in his figure of the stickleback, similar features were probably present. The 

 salmon, at any rate, would thus appear to be more heterocercal than the wolf-fish. 



Notochord. — The notochord in the newly hatched A narrhichas (in January) is similar 

 externally to that of the salmon — that is, it has the usual pointed anterior end, with the 

 downward curvature toward the oesophagus. The structure of the chorda also corresponds, 

 though on the whole in the wolf-fish it seems more firm, since it preserves its circular out- 

 line (in section), and its cells appear to be smaller. The notochord of the salmon is prone 

 to collapse, a feature, however, that may be due to the preparations. Posteriorly, again, 

 a decided difference exists, since the notochord in the wolf-fish is at this stage quite 

 straight. The straight notochord of the young Clupeoid, ^ inch in length, is remarkable 

 for the regular serial arrangement of the large chambers extending from end to end. 

 The post-larval condition is thus like that of the earlier larva in this feature ; but the 



* Ann. des. Sci. Nat., t. xvi. p. 184, pi. iii. fig. 42. t Huxley, op. cit. 



