128 REPORT — 1860. 



animals from embryonic data, however, is still more artificial ; it takes only one 

 small group of properties of the animals, and just a group which, by its being con- 

 fined exclusively to individuals, forbids by itself the taking account of other pro- 

 perties. There are so many striking examples of different development in animals 

 related as nearly as possible, that by these alone the exclusive use of embryology 

 as a basis for classification is defended. And if the fact of frogs developing with- 

 out the intermediate stages of tadpoles be true (and I have no reason to doubt it), we 

 have in one and the same species differences of development which would in other 

 classes suffice to establish orders. By this very instance it is shown that embry- 

 ology also has only a relative value as zoological character. Our next inquiry ought 

 to be directed here, as well a 5 in all other eases, towards the establishment of the 

 characteral standard of embryology. Nature herself assists ns in the rightly 

 weighing of this character of animal bodies, as almost in all cases it serves only to 

 confirm and strengthen relations which have been found by other methods. 



While there is scarcely any difficulty in giving to embryology amongst the other 

 sets of properties its right place with regard to the classification of animals, there 

 is, I should not like to say difficulty, but some seemingly perplexing complexity of 

 phenomena and relations, when we are to make out the true bearing of embryology 

 on animal morphology. Here I have to answer two questions : How must we look 

 upon animal forms P and secondly, Are we allowed to explain analogous pheno- 

 mena by methods not correlate to each other ? Animal morphology, as the science 

 of animal forms, has to explain these, that is to say, to bring them back to laws. A 

 law manifested on different forms cannot be that of cause and effect, but only one of 

 a constant repetition of the same phenomena under seemingly different conditions. 

 The object of animal morphology therefore will be to show the constancy with which 

 certain organs appear in certain groups of animals, and to showthat the relative posi- 

 tion of these organs is always one and the same in the larger and lesser groups. With 

 regard to the first part of these inquiries, there can be no doubt as to the utter failure 

 of embryology. Nothing but a simple anatomical investigation can tell us whether a 

 certain organ or system of organs is present in a certain division of the animal 

 kingdom or absent ; and respecting the second part of our morphological researches, 

 I am equally inclined to doubt whether embryology gives us an insight into the 

 anatomical specialities of a somewhat more complex animal by anything else, but 

 by bringing before us certain forms which are not quite as complex as the animal 

 which we dissect. And here we need not take embryological data ; we have before 

 us in every type of animals a whole series of more and more diversified forms, which 

 by themselves offer that same series of simpler forms which we find in the indi- 

 vidual, and even more clearly manifested, because an embryo is always endowed 

 with certain individual or specific peculiarities, which we cannot at present account 

 for at all. With respect to my second question, the embryologists say that two 

 organs which are developed in two different ways cannot be considered homologous. 

 Now, here I have to give a somewhat similar answer to that which I gave with 

 respect to the embryological classification. The homology of parts is determined 

 by the constant relative position of the organs in one and the same type. An artery 

 which rims up along the mesial line of the cervical vertebrae, is homologically dif- 

 ferent from an artery which runs along the jugular vein and the pneumogastric 

 nerve. The morphological relations of a certain class cannot be determined but by 

 comparing full-grown individuals, as all the organs do not work to the purpose of 

 these individuals before the development is finished. And in this respect I must 

 deny any influence of embryological researches on morphological questions. There 

 is, however, another set of questions frequently brought before the inorphologist, 

 namely, whether two homologous organs are developed in the same way. It is 

 easily seen that their homology must have beeu determined beforehand. It is of 

 course of the greatest interest to know the differences of the development of the 

 same organ in different representatives of the same type. But they show nothing 

 more than the wonderful facility with which Nature arrives at the same results by 

 different ways. They give us additional proofs of that immense richness of means 

 with which "the Creator of all animal bodies works out his plans. 



On (he Deglutition of Alimentary Fluids. By Professor Corbett, M.D. 



