THE DOGFISH 



19 



at birth may measure from twenty-five to thirty centi- 

 meters in length. If the female dogfish is killed and 

 the young within her are quickly removed by what may 

 be termed a crude Caesarean operation, the pups, as 

 they are called, if handled gently, remain momentarily 

 passive even when immersed in sea water. After they 

 have been for a fraction of a minute or so in their watery 

 environment their gill movements begin and they will 

 start swimming, but with somewhat unsteady equilib- 



* Life * 

 i ft* > 



f 



*.« 



* 



Fig. 14. Dermal melano- 

 phores of a newly born smooth 

 dogfish, Mustelus, in the pale 

 phase, pigment concentrated. 

 Parker, Biol. Bull., 1936, 70, 

 pi. 1, fig. 3. 



Fig. 15. Dermal melano- 

 phores of a newly born dogfish, 

 Musteius, in the dark phase, 

 pigment dispersed. Parker, 

 Biol. Bull., 1936, 70, pi. 1, 

 % 4- 



rium. In a very short time, however, they are indis- 

 tinguishable from pups normally born. 



Fully formed young dogfishes when first removed from 

 the female are darkish in tint, but they will respond 

 immediately to the tone of the environment. In one 

 instance three newly born pups were put at once into 

 a black-walled illuminated tank. In twenty minutes 

 they had darkened perceptibly and in a little less than 

 an hour they were fully dark. Others that had been 

 put directly after birth into a white-walled tank were 



