Chap. VII.] THEOKY OF NATURAL SELECTION. 295 



the case with some members of trie same order. Why 

 Cercopithecus, considering its habits whilst young, has 

 not become thus provided, it would be difficult to say. 

 It is, however, possible that the long tail of this monkey 

 may be of more service to it as a balancing organ in 

 making its prodigious leaps, than as a prehensile organ. 



The mammary glands are common to the whole class 

 of mammals, and are indispensable for their existence ; 

 they must, therefore, have been developed at an extremely 

 remote period, and we can know nothing positively about 

 their manner of development. Mr. Mivart asks : " Is 

 it conceivable that the young of any animal was ever 

 saved from destruction by accidentally sucking a drop 

 of scarcely nutritious fluid from an accidentally hypertro- 

 phied cutaneous gland of its mother ? And even if one 

 was so, what chance was there of the perpetuation of such 

 a variation ? ' : But the case is not here put fairly. It is 

 admitted by most evolutionists that mammals are de- 

 scended from a marsupial form ; and if so, the mammary 

 glands will have been at first developed within the 

 marsupial sack. In the case of the fish (Hippocampus) 

 the eggs are hatched, and the young are reared for a time, 

 within a sack of this nature ; and an American naturalist, 

 Mr. Lockwood, believes from what he has seen of the 

 development of the young, that they are nourished by 

 a secretion from the cutaneous glands of the sack. Now 

 with the early progenitors of mammals, almost before they 

 deserved to be thus designated, is it not at least possible 

 that the young might have been similarly nourished ? 

 And in this case, the individuals which secreted a fluid, 

 in some degree or manner the most nutritious, so as to 

 partake of the nature of milk, would in the long run have 



