LOWER JAW DEVELOPED. 121 



little cost, and that becomes such a valuable 

 article of food." 



In various creatures the progress of de- 

 velopment is different ; thus, for instance, 

 in the human baby, the first portion of the 

 body developed is the lower jaw, and this 

 for an obvious reason, because the most 

 material want of the baby is to obtain the 

 mother's milk by suction. Now, if the lower 

 jaw were not solid and firm, in vain would it 

 try to suck. 



Now, in the case of the fish, nature has 

 kindly packed up all the nourishment that it 

 will want for some six or eis:ht weeks in a 



o 



neat little bag or parcel, which she has affixed 

 to the body of the fish in such a manner that 

 it shall be gradually absorbed into the general 

 system ; the fish does not suck milk like a 



