204 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



We are informed by very high authorities that man, for instance, is de- 

 veloped from an ovule about the 125th of an inch in diameter, which 

 differs in no respect from the ovules of other animals. Even within the 

 limits of the mammalia, the phrase " differs in no respect from the 

 ovules of other animals" is obviously inaccurate if a careful and just 

 comparison of the figures of the ova of various genera and their dimen- 

 sions, &c, as given by specialists, are compared together. That hack- 

 neyed comparison of the gill arches of the various groups of vertebrates, 

 indicating as it does, and as every one will be ready to admit, an im- 

 portant morphological law, namely, community of descent, we cannot 

 help but be incredulous when it is asserted, as it often is, that at a cer- 

 tain stage it is nearly or altogether impossible to distinguish an embryo 

 human being from a fish or dog of the same relative stage of develop- 

 ment. If some of the most enthusiastic defenders of this type of evo- 

 lution run mad had stuck conscientiously to the word " nearly" in 

 order to qualify their assertion of the appearance of identity which they 

 have mostly discovered upon comparing the embryological figures of 

 careful laboratory investigators, we should not feel called upon to write 

 the present paragraph. Of such an identity, perfect in detail, I defy 

 any honest investigator to produce proof. It would, on the other hand, 

 be an easy matter for specialists to produce abundant evidence that 

 even within the limits of small and restricted groups specific differ- 

 ences already make their appearance with the first steps of segmenta- 

 tion, leaving out of account all other purely morphological differences, 

 which, conscience knows, are sufficient in themselves to break up the 

 foundations of the doctrine of identity so glibly retailed by these care- 

 less writers. It has been noted that the segmentation of their germs 

 will serve to mark the genera and species. I will go a step further and 

 assert that there are numerous features, properly characters, which will 

 serve the same purpose at various stages, and that at no stage can it be 

 said that there is a positive identity even in closely allied genera or 

 strongly marked species. Embryological differences have not been well 

 enough studied in slightly marked varieties or species, to say much of 

 these. But genera ought, in all conscience, to be close enough together 

 to refute the validity of the " uniform germ theory." Here we find in 

 every case great numbers of characters which may be stated in words, 

 and many of these even become the most positive differentia) when a 

 certain embryo is compared with the embryos of something else. Vast 

 numbers of details must be considered as affecting this too readily as- 

 sumed identity, not the least of which is form; perhaps this latter is 

 really the most important. So long, then, as the somewhat similar germs 

 of different animals produce different species, we shall or ought to hold 

 to the doctrine that the protoplasm of which a man is made is different 

 from that of which the body of a dog or a fish is composed. 



I do not wish to be understood as denying the possibility of variation 

 in the nature of the protoplasm of different germs which have been de- 



