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 Gastrosteus, 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. cit., p. 178) recommends (rastrosteus 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, eg., 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. Empryonic, Larvat, AND Post-LARvAL CoNnDITIONS OF THE Foop FisHes.t 
Trigla gurnardus,t 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 (Pl. XII. fig. 1), is a glassy transparent 
form with a considerable yolk-sac, the oil-globule (egy) 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, poe), 
* 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). 
+ 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 struetural grounds 
for the remark. § Mr Scorr found ova of this species in the Moray Firth in January. 
