THORNBACK. 
1107 
the Mediterranean and the Black Sea (Pallas), and 
it has been found off Madeira (Gunther). 
In the island-belt, of Bohusl&n Thornbacks both 
young and old are taken all the year round. During 
winter, however, they are less common, and the fisher- 
men state that at this season the Thornback repairs to 
deep water. In spring and summer it is very plentiful 
off the coast, where it seems to prefer water of a mo- 
derate depth a and with a sandy bottom. It lives almost 
invariably at the bottom and extremely seldom ascends 
to a higher level. Its food consists of small fishes, 
crustaceans — crabs, lobsters, shrimps, etc. — mollusks, 
Annelids, Echinoderms, and Actinice \ 
Throughout the summer the females contain deve- 
loped ova; but according to Fries only one egg is laid 
at a time, and the period of oviposition for each female 
must consequently be of long duration. Fries observed 
that, on opening old females in summer-time, the egg- 
clusters in the ovaries are found to be considerably 
tumid, the several eggs showing different grades of 
development, from the size of a pea to that of a plum. 
In the two oviducts however — each of them dilated 
below into a uterine organ — he never found more than 
a single egg, and this already invested with the sin- 
gular corneous shell. When one of the uteri contained 
an egg, the other was empty. The ovum is of the form 
normal among the Rays, rectangular, with the four 
corners prolongated in its longitudinal direction, and 
according to Malm 0 is 55 — 57 mm. long and 40 mm. 
broad, but including the filaments at the corners 110 
— 115 mm. long. Fries once found a female Thorn- 
back with a half expelled egg in the cloaca. On ex- 
amination the protruding end of the egg proved to be 
open, the larva having already left the shell. He dis- 
sected the specimen, and saw that the left uterus was 
empty, but that in the right there lay a recently de- 
scended ovum, the shell of which was still very soft. 
In this case it was consequently evident that the em- 
bryo had freed itself from the egg immediately on the 
expulsion of the latter. Malm, on the other hand, 
never found a viable foetus, scarcely a distinct embryo, 
in newly deposited ova, whence he inferred that the 
development of the embryo does not commence until 
the egg is laidfi The process of development may thus 
vary in its acceleration; but by far the greater number 
of the eggs found after liberation are empty. During 
their early life, according to Kroyer, the fry keep to 
the shallows of shelving coasts. 
The Thornback is taken on long-lines and in Floun- 
der-nets, less frequently in the seine. As an article 
of food it enjoys a good reputation in Great Britain 
and Ireland, especially in the latter country 0 ; but 
in the island-belt of Bohusl&n, according to Ekstrom, 
it is regarded as one of the poorest fishes. It is hardly 
ever eaten fresh there, at all events by the islanders, 
who instead dry the flesh in the open air on flakes 
( gdllar ) or platforms, constructed in elevated situations. 
After drying it is sold to the peasants of the agricul- 
tural districts, who use it as a substitute for lutfisk f at 
their Christmas festivities, and consider it good eating. 
Besides knaggrocka (Spiny Ray) this species bears 
in the island-belt of Bohuslan the names of piggrocka, 
as adult, and rockhok and peruk , while young. On the 
coast of Scania it shares with the following species the 
name of torr-borr, according to Lilljeborg a corruption 
of the Danish Tcerbe. (Fries, Ekstrom, Smitt.) 
a According to Malm the full-grown Thornback is only seldom found in less than. 14 fathoms of water. 
6 See Olsson, Fiskarnes foda, Lunds Univ. Arsskr., tom. VIII, 1871. 
c Ofvers. Vet. Akad. Forh. 1876, No. 3, pp. 94, 95. 
d Gbgs, Boh. Fauna , p. 607. 
e See Day, 1. c., p. 345. 
f Dried Cod etc. soaked in lye before cooking. This is still a staple course in Sweden at Christmas and on other feast-days. Tr. 
