49 o ANIMAL LIFE-HISTORIES 



duces a single well-developed young one at a birth, which is 

 tended by its mother with the most jealous care. It may fre- 

 quently be seen riding upon her back, and under these circum- 

 stances she comes very frequently to the surface, seeming to be 

 aware that her offspring requires to take a fresh breath more 

 frequently than she does herself. 



Ruminants (fig. 1003) usually give birth to a single young one, 

 or more rarely to two. The power of chewing the cud is not 

 at first possessed, since only the fourth or chemical division of 

 the stomach (abomasum) is properly developed (see vol. ii, p. 

 169). This is quite able to deal with milk, to which diet the 

 young animal is necessarily restricted till such time as the diges- 

 tive organs are fully developed. The social habit, here very 

 typical, is associated with interesting defensive tactics, such as 

 setting sentinels to guard the feeding herd (see vol. ii, p. 365). 



ELEPHANTS (PROBOSCIDEA). As in the case of Ruminants, 

 a single young one as a rule is produced at a birth in these 

 gregarious animals, and from the first it is well able to accom- 

 pany its mother in her rather extensive wanderings in search of 

 food. It is scarcely necessary to remark that the young animal 

 sucks with its mouth, and not with its trunk, though the contrary 

 was long believed. There are but two milk-glands, placed on the 

 chest. 



SEA-Cows (SIRENIA). Both in the Dugong (Halicore) and 

 the Manatee (Manatus) there is but a single young one, born 

 in a well-developed state, as might be expected in such thor- 

 oughly aquatic animals. There is a single pair of milk-glands, 

 placed on the chest, and the mother has a curious habit of 

 holding her offspring firmly by means of one flipper during the 

 operation of sucking, swimming along at the same time with its 

 head and her own above the surface. 



WHALES, PORPOISES, &c. (CETACEA). Of all Mammals these are 

 by far the best adapted to an aquatic life. There is usually only 

 a single young one, which, from the nature of the case, is born 

 in a well-developed condition, and perfectly able to swim. Flower 

 very justly remarks: "This state of relative maturity at birth 

 reaches its highest development in the Cetacea, where it is 

 evidently associated with the peculiar conditions under which 

 these animals pass their existence ". The two milk-glands are 

 placed far back on the under side of the body, the teat of each 



