240 INTRODUCTION TO ZOOLOGY. 



comparative anatomist. These little fishes had devoured some 

 larger ones of a different species, which had been confined in 

 the same vessel with them, eating off their hodies what they 

 required at one time, and returning, in the Abyssinian fashion 

 described by Bruce, for another supply when wanted. 



Fig. 195. EGG-BAG, WITH YOUNG SHARK. 



SQUALID^:, RAIID^E. The Sharks and the Rays, though 

 differing so much in external form, belong to a group of fishes 

 of which the gills are fixed, and the water, passing through 

 the mouth, escapes from the gills by a series of longitudinal 

 incisions. The ova, which are few in number, are not depo- 

 sited on the sand or gravel, but each egg is enclosed, for 

 greater safety, in a horny case, attached by long tendrils to 

 the larger sea-weeds; and among the Sharks of the largest 

 size, some bring forth their young alive. The empty egg-cases 

 are frequently found on the sea-shore, and are well known by 

 the name of " sea-purses," "mermaids' purses," and other 

 local terms. The longer and narrower-shaped (Fig. 195) 

 belong to the Sharks and Dog-fishes; the broader and shorter 

 ones to the Skates or Rays. Water is admitted into them 

 by means of a slit at each end of the purse. In two large 

 clusters* dredged up in Strangford Lough, and sent to the 

 Belfast Museum, the cases were obviously of three very dis- 

 tinct ages, the most recent being yellowish, semi-transparent, 

 and the contents resembling those of a newly-laid hen's egg. 

 Our figure, which is copied from that given by Mr. Yarrell, 

 represents the case laid open, and the young Dog-fish 

 attached to the * i yolk, ' ' or membraneous bag of nutriment, 

 which is gradually absorbed as the growth proceeds. 



* They were regarded as the ova of the Large-spotted Dog-fish. W. 

 Thomson, in Annals Nat. Hist. vol. xiv. p. 23. 



