360 Mr. R. Hill's Contributions to the 



when deposited within the reach of the light and heat of the 

 summer sun. Two narrow shts in the capsule, the provision we 

 have referred to already, allow of the admission of aerated water, 

 and of the expulsion of the fluid, when the oxygen has been 

 consumed in sustaining the embiyo. For a time the young fish 

 is nom-ished by the vitellus attached to the body, till it has 

 acquired the power of taking food by the mouth, when the fluid 

 contained in the depending sac being taken within the abdomen, 

 just as the yolk which nourishes the bird within the egg is ab- 

 sorbed at the moment of hatching, the matured Dog-fish escapes 

 by the fissure which opened near where the head of the folded 

 embryo was situated. 



There is another interesting provision observed in this class 

 of Cartilaginous Fishes. The oi-dinary gills are not fitted, at the 

 early stage of life, for the ofiice of respiration. To meet this 

 emergency there are filaments provided at each branchial open- 

 ing, containing a single minute reflected vessel, in which the 

 blood is submitted to the action of the aerated water. These 

 appendages are only temporary. Some short time after the 

 embryo has been excluded, the filaments are gradually absorbed, 

 and respiration is carried on by the true gills. 



In everything connected with the structure of the egg, we 

 see the provision made for hatching it, independent of the parent ; 

 the arrangement for suppljdng it with air from the influent waters, 

 on the one hand ; and the appliances for securing it near the 

 surface, within reach of the sun's rays, and within the increased 

 temperature of the shore, on the other. The parent having de- 

 posited the egg, already vivified by previous contact, when the 

 male and female hunted together in social packs, it is left to the 

 accident of tides and agitated seas to be matured and hatched in 

 due season. 



The Scymnus spinosus, or Spinous Shark, is not so well known 

 on the British coast as the Spotted Dog-fish, but it is common 

 enough in the Mediterranean with the Squalus Nicensis and the 

 Huraantin or Centrina. The Centrina inhabits muddy bottoms, 

 and the Nicensis aff'ects waters of a particular degree of tempera- 

 ture; Risso says of 10 degi'ees of Reaumur, equal to 53 of 

 Fahrenheit; and that it is caught with particular baits at a 

 thousand metres below the surface. When the spinosus is taken 

 on the Cornish coast, it is caught either in trawl-nets or on hooks 

 sunk down for conger-eels, and baited with cuttle-fish. The fisher- 

 men describe its action as most powerful in the water. As they 

 are obliged to let him run with a line four times to the bottom 

 before they can hamper him with a sliding noose, let down over 

 the line to his tail, Mr. Yarrell therefore remarks, that as these 

 and the trawl-net only do their ivork at the bottom, we may con- 



