IN THE LIMBS OF MAMMALIA. 15 



If the previous reasoning is correct, it follows that the anterior and posterior regions of 

 the vertebrate body, consequently of our own, are anterior and posterior repetitions of 

 each other, but in opposite directions, like the right and left sides. 



At first sight, nothing is more improbable to our thought or revolting to our feelings, and 

 the evidence must be strong to overcome this natural repugnance to the relationship. 



Yet why should it be objectionable, any more than that neither anatomy nor microscopy 

 nor chemistry can detect the slightest difference between two human brains to indicate 

 that one of them was the agent of a wicked and depraved, the other of a noble and lofty 

 soul ? It is the universal distinction between morphology and teleology, between the thing 

 as it is made and as it is used ; and when this distinction is once rightly appreciated, we 

 shall be no more shocked at the morphological identity of the two ends of our corporeal 

 frame than we are, or ought to be, at the close anatomical relationship between the disgust- 

 ing ape and ourselves, remembering in both cases that it is the use alone which can ennoble 

 or debase. 



Our evidence is as yet by no means complete as regards all the organs of the vertebrate 

 body, but enough has been brought out to very strongly confirm the principle. 



As was implied when treating of the general law of polarity, we must, if this is acknowl- 

 edged, recognize a new relation of homology between parts representing each other at the 

 two ends of the longitudinal axis, and, in fact, on opposite sides of the longitudinal centre, 

 similar to, but by no means so obvious as, that existing between the right and left sides. 



This is not the " serial homology," of Professor Owen, for he regarded all the vertebrse and 

 their appendages as simple repetitions of each other from one end of the body to the other, 

 without recognizing the fact, which we shall see most clearly in the limbs, that the anterior 

 and posterior organs of the body are repetitions of each other, but in opposite directions ; so 

 that the term " homotype," by which he designated parts serially homologous, really applies 

 only to such as repeat each other on one and the same side of the longitudinal centre, and 

 for the new relation between parts on opposite sides of this point a new term must be 

 found. 



Adopting the phraseology of Professor Owen we may call all parts which repeat each other 

 as opposite ends of any axis " antitypes," and the antitypes of the lateral axis " latitypes," 

 of the vertical axis " vertitypes," and of the longitudinal axis " longitypes," which will be 

 specially characteristic of the three higher sub-kingdoms, Mollusks, Articulates, and Verte- 

 brates, respectively, while the homologous diverging segments of the Radiata may be called 

 " raditypes." In the Vertebrates the head and pelvis are longitypes ; and the thorax and 

 abdomen bear the same relation. This is a very general homology. 



There will now arise, with reference to the longitypes, or the homologous parts in the 

 anterior and posterior regions of one animal, a question similar to that concerning corre- 

 sponding parts in two different species ; which was whether they can be to the same extent 

 homologous in animals bearing different degrees of zoological relationship: for example, the 

 anterior extremities of all Vertebrates are homologous ; but surely the arm of the monkey 

 is more closely related to the fore-leg of the cat than either is to the flipper of the porpoise 

 or the pectoral fin of the fish ; and now, since the main axis or vertebral column begins 

 to be formed at what is afterward the point of division between the fore and hind regions 

 of the body, and the head and pelvis are situated at or near the ends of that axis, it does 

 not seem possible that these parts can be as strictly homologous in animals having a 

 different number of vertebras as in those with the same number : in other words, the heads 

 or the pelves of two animals may be cranial or pelvic modifications of vertebrse without 

 being such modifications of the same identical vertebrse. 



