98 The Origin and Transformation of Animals. 



fundamental characteristics of the group of which the new crea- 

 ture will form a part." 



We must refer the reader to M. Quatrefages* agreeable 

 volume for further details on this branch of the subject, and pass 

 to the consideration of a few points in the development of the 

 egg of the mammalia. Here our author tells us the heart soon 

 makes its appearance, accompanied by arteries and veins, and 

 soon after it the nervous system, the digestive tube appearing 

 more late. This order of succession is directed by the method 

 of nutrition, and it is inverted among the invertebrata, where 

 the digestive apparatus precedes the circulatory. In watching 

 the process of transformation, " every day, every hour, the scene 

 changes, and this instability effects essential as well as necessary 

 parts, etc. . . Here cavities partition themselves into distinct 

 chambers, or extend themselves into canals ; and these, in their 

 turn, are filled up and converted into ligaments ; films are rolled 

 up into tubes ; isolated parts solder themselves together into 

 continuous organs, or uniform masses divide themselves and 

 form several organs. At the same time, relations and propor- 

 tions change each instant. Parts which had been almost corn- 

 founded, separate and become strangers ; others, which had 

 been separated, approach and contract intimate union. Organs 

 with temporary functions, grow, increase rapidly, acquire an 

 enormous size, and then become atrophied, and disappear. 

 Others stop at a given moment, while all grows around them. 

 They retain their place, and will be found in the adult, where 

 they have no other apparent part than to bear witness to a state 

 of things which no longer exists." 



Having got out of the egg and been born, the young mam- 

 mal experiences transformations,* the proportions of the several 

 parts altering at each stage, that of puberty being highly in- 

 teresting and important. MM. Andral and Gavarret state that 

 at an early age boys and girls respire with equal vigour. Before 

 puberty M. Quatrefages calls them neither males nor females, 

 but neuters. " But as soon," he says, " as the sexes are charac- 

 terized, the respiration of the young man exhibits a redoubled 

 and rapidly augmenting activity, while in the young girl and 

 young woman this function remains stationary. About the age 

 of thirty the former burnsf about one hundred and seventy or a 

 hundred and eighty-six grains of carbon in an hour. Subse- 

 quently, when the progress of age, and its accompanying trans- 

 formation, cause the two sexes to approach by effacing their 

 more salient characteristics, the respiratory activity of the 



* M. Quatrefages entitles the chapter from which these remarks are taken 

 " Transformations des Mammiferes hors de l'ceuf." Thus he does not follow the 

 nomenclature which he recommends, and according to which these changes would 

 be metamorphoses. 



f The non-chemical reader may he reminded that respiration is a process of 

 combustion. 



