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



alcohol, it was found necessary in the case of certain embryos to remove the yolk. In such com- 

 paratively large forms as Cyclopterus, Cottus, Anarrhichas, and Gastrostcus, the yolk became so dense 

 in the hardening process that the razor of the microtome would not pass through it ; hence, by 

 dissecting off a portion of the yolk-sac, the enclosed yolk could with care be removed en masse. 

 Whitman {op. eit., p. .178) recommends Gastrostcus as especially suitable for sections, forgetful of the 

 fact that the yolk-mass presents peculiar difficulty to the microtomist* — in contrast to the yolk-mass 

 of more delicate ova, such as the cod, whose yolk is cut with ease by the razor. Ova which contain 

 large oil-globules, e.g., Trigla and Molva, are not reliable for cutting, the alcohol removing their 

 constituent fluid, and leaving large empty cavities in place of the globules. 



XI. Embryonic, Larval, and Post-Larval Conditions of the Food FiSHES.t 



Trigla gurnardus,\ L. — In dealing with the ova of this species, it has as a rule 

 been found at St Andrews that the ripe females are considerably larger than the males, 

 but whether this is due to the fact that the males, as in some other fishes, e.g., the 

 salmon, become earlier mature, or to other circumstances, is at present undetermined. 

 The rate of development of the embryo depends much on the temperature, thus ova 

 fertilised on the 6th May hatched on the 13th day, while the embryos escaped from the 

 eggs on the 6th day, respectively on 17th June and 5th July 1885. The spawning 

 period of this form is thus considerable, viz., from April to June.§ 



The young gurnard, on emergence (PI. XII. fig. 1), is a glassy transparent 

 form with a considerable yolk-sac, the oil-globule (og) in which is conspicuous at 

 the posterior angle, and is surrounded by a thickened layer of protoplasm (p). 

 Numerous round pigment-corpuscles of a dull yellow or olive colour, often apparently 

 dull greenish, are scattered over the head, dorsum, and latero-ventral region, but 

 they do not extend to the tip of the tail. The dorsal margin of the embryonic 

 fin has finely ramose, dull yellow, pigment-spots, with a few intermingled black 

 corpuscles. These proceed within the dorsal edge, and may be traced down to the body 

 line, a short distance in front of the tail, finally intermingling with the branched pigment 

 on that portion of the animal. A similar pigmented area occurs along the ventral fin for 

 a short distance. The coloration of the pectoral fin (pf) is very striking, an arch of 

 pigment-corpuscles passing across the base of the organ, which, as in the young cod, is 

 now erect. Over the yolk, as already noted, many stellate yellowish and a few 

 black corpuscles occur, and they often anastomose. We have seen that this 

 colouration of the yolk-envelope is characteristic of certain species, the gurnard being 

 one, while in others, e.g., cod and haddock, this feature is absent. Besides the opercular 

 aperture, a single gill slit (?) at this stage occurs above the heart (PL VIII. fig. 8,poa), 



* Wenckebach, who killed the embryos of Perca in corrosive sublimate, and stained in picro-carmine, alludes to 

 this character of the yolk — " the embryos being very small, and the yolk extremely hard in the preserving reagents . . . 

 satisfactory sections are difficult" (No. 157). 



t The order of convenience only has been followed in this section. 



t Day (Commercial Fishes of Brit, p. 77) states that the gurnard probably spawns twice a year, viz., in mid-winter 

 and mid-summer. If he means that each individual fish spawns twice, there would seem to be no structural grounds 

 for the remark. § Mr Scott found ova of this species in the Moray Firth in January. 



