338 COMPARATIVE ANATOMY 



to the discovery of these laws; it becomes a true science having 

 its own object. It remains dependent upon zootomy for the mater- 

 ials- which it borrows therefrom, but it is no longer content with 

 retouching, with rearranging its facts; it draws from them new 

 conclusions. 



Here, as everywhere in biology, these so-called laws cannot be 

 considered as directive principles, as active forces, but only as 

 general propositions summarizing a large number of the facts of 

 observation. The following are the most important of these propo- 

 sitions: 



Law of connections. If we compare the characteristics which the 

 same organ presents in a more or less extended series of animals, 

 we perceive that these characteristics are more or less variable 

 according to their nature: color and form are in general very much 

 so, structure, the relations of contiguity, are fairly so; but there is 

 one which is almost invariable, and that is connection, or, in other 

 w r ords, the relations of continuity. For example, the pelvic fins of 

 fishes called jugulars are greatly displaced, since they are carried in 

 front of the pectoral fins, but the nerves and arteries which they 

 receive are given off, nevertheless, from a point situated behind 

 that from which the nerves and arteries of the pectoral fins start; 

 the lungs of serpents elongate to form cylinders which are placed 

 one behind the other, the posterior far towards the rear of the body 

 in a region very different from that which it occupies in other ani- 

 mals; but their point of insertion in the pharynx, the glottis, re- 

 mains unchanged; the statocysts of lamellibranchs are situated 

 in the foot, far from the place w r hich they occupy among the other 

 mollusks, where they are near the cerebral nervous centres, but 

 their nerve connects them with that centre, a direct emanation of 

 which they therefore remain. This principle of connection is equi- 

 valent to considering organs as attached at a fixed point, which is 

 their place of origin, by an elastic cord, which allows them to make 

 all changes of place without losing their connection with the fixed 

 point. This cord is a thread of Ariadne which permits regaining the 

 point of departure despite the most distant migrations. In tracing 

 back these organs among all animals to the place of origin which 

 their connections indicate, an important share of their differences 

 is made to disappear, and their comparison is made clear. This is 

 the principle of Geoffroy Saint-Hilaire. 



Principle of the balancing of organs. It is well known that the 

 relative development of organs in the body is very different among 

 different animals. Geoffroy Saint-Hilaire remarked that , when one 

 organ attains an excessive development, one or more of the others 

 suffers a corresponding atrophy. This principle results from the 

 fact that the necessities of nutrition do not allow a number of organs 



