THE SOUTHERN SEA LION 297 



It will be observed that the number of the stones varies, and the condition. The 

 stones are not necessarily beach-worn pebbles; they may be comparatively sharp 

 fragments of cliff talus, although they show some signs of the grinding to which they 

 have been subjected. Three hypotheses have been advanced to explain the presence of 

 the stones : it may be that all are correct, and there is at least no doubt that the stones 

 will have some of the effects suggested in (a) and (b), if only incidentally. 



(a) They perform the same function in the remarkably muscular stomach of Otaria 

 as does grit in the gizzard of a fowl, namely, to assist in pulping the food. 



{b) The stones are ballast, taken in to trim the sea lion in the water. It is a fact that 

 the hind-quarters are very light in proportion to the fore-part of the animal and that 

 the pup, when learning to swim, seems to be "by the head" in nautical phraseology, 

 that is to say too heavy forward. 



{c) The stones serve to grind up and destroy the Nematodes with which the stomach 

 is invariably infested (Hahn, 1884). 



The stones either wear away or are thrown up, for, as has been stated, the largest 



stones are usually from the largest sea lions ; but I have never myself seen the act of 



regurgitation. Nevertheless the animal is quite capable of it, since I have seen a female 



vomit after a fit of coughing and the stomach contents were thrown several feet. It 



may be remarked that the fur seal of the Falkland Islands does not normally ingest 



stones. 



SEXUAL MATURITY 



Neither sex shows the facies of the fully adult until the sixth year. The males of 

 the fifth year are large animals ; they may attain a total length equal to that of the smaller 

 adults, but the head and neck, although well developed, fall short of the massive 

 structure of the bull (Plate VII, fig. i). Sections of the testis of a fifth year male shot 

 in January show spermatozoa, but not in the same quantity as the testis of an adult 

 male shot at the same time, and in the latter the tubules are larger. 



The fifth year male may be described as sub-adult, but even if he is capable of 

 service he would have no chance in a contest with an adult, and indeed these sub-adults 

 are visibly afraid of the bulls. In the skull the onset of adolescence is marked by a rather 

 rapid increase in the proportion of the zygomatic width to the length of the skull as 

 well as by the osteological characters described on p. 284. 



The female becomes sexually active about the end of the fourth year. During that 

 year the colour of the coat and the form of the pterygoid region of the skull give indica- 

 tions of the approaching change, but the ovaries are only very slightly enlarged. The 

 important change takes place between the fourth and the fifth years. 



There is an alteration in the form of the skull, as is shown by the relatively increased 

 length of the palate and the greater zygomatic width, and the ovaries become active. 

 Three females of this stage were killed in July, Nos. looi, 1030 and iioo, and of 

 them, one had every appearance of having aborted, one was pregnant and the third 

 had ovulated. They were all sexually mature. 



The time and place of the fertilization of the virgin cows are obscure ; I have never 



