of the Fisher// Board for Scotland. 
301 
somewhat younger than the one figured by me in figs. 16 and 17. The 
last figure was that of a newly hatched skate. 
In dealing with such an extensive subject as the development of the 
skate, it was necessary that some plan of treatment should be adopted, all 
the more as the amount of space and the number of plates of figures at 
my disposal were strictly limited. Seeing that almost no figures of skate 
embryos, especially early stages, have been published till now, it was 
natural that this branch of the subject should receive attention. A 
detailed account of the development of the internal organs would have 
occupied very much space, and have required an extensive series of 
figures. In the end this would have had little practical value. 
Other points to be noticed more especially were the breeding and spawn- 
ing seasons, the characters of the egg-cases or purses of different species of 
skate, the duration of development, and such points in the physiology of 
the embryo as could be determined. 
Unfortunately I am at present unable to give much account of the 
actual time the development occupies. Many embryos, which would ere 
this have hatched out, were lost in a storm during the winter. This 
much can be said, viz., that the development occupies a longer period 
than is usually supposed, and for the blue skate (E. batis) I should incline 
to the belief that development requires nine or ten months. The oldest 
embryo I have yet obtained is figured life-size in figs. 16 and 17; the 
yolk-sac attached to the embryo weighed (in spirit) 22 grams, or about 
f of an ounce. The rate of development is very different in summer and 
in winter. In winter the temperature of the water varied between 
and 6° C, while it rose to 11° and 12° C. in the early summer months. 
Under the latter conditions development proceeds as rapidly again as in 
winter, and a stage reached in three months in winter is attained in less 
than two in the summer. The material * at my disposal was all that 
could be wished, and thus the dimensions of this paper are only limited 
by considerations of space and time. 
The Breeding and Spawning Periods of the Skate. 
To these points but little attention has hitherto been paid, and in the 
literature one finds very little information. In volume ii. of his British 
Fishes £)r Day has recorded all that he could learn about the breeding 
and spawning of the skate. 
It must be mentioned that the period of ' ripening ' and fertilisation of 
the egg much precedes that of its oviposition. For some weeks at least 
the egg undergoes development without the maternal oviduct, and there 
it normally lies until the first traces of the embryo appear. It is then laid 
by the mother-skate, and undergoes its subsequent long development at 
the bottom of the sea. Eggs taken from the parent skate, as soon as or 
after their complete enclosure in the purse, will develop in a perfectly 
normal fashion in sea- water. The plan adopted by me was to place the 
purses taken from the parent-skate in perforated fish-boxes in the harbour, 
and if the purses were good at the start, there was, except in the case of 
those of R. circularis, very little mortality subsequently. 
The purses of ft. circularis are very tender, and most probably they are 
only deposited by the parent skate in perfectly sheltered bays, and where 
* To Mr George Sim, A.L.S., Aberdeen, and to Messrs J. Murray and W. Mair, 
Fishery Officers of the Fishery Board for Scotland, I am chiefly indebted for the 
material used in these investigations. My thanks are also due to Mr P. Jamieson, 
of the Scientific Staff of the Scottish Fishery Board, for all the trouble and care he 
has bestowed on the rearing, &c, of the embryos. 
