EA.RLY ONTOGENETIC PHENOMENA IN MAMMALS. 241 
the true gastruhi stage and the post gastrula stage, whicli 
latter is the growth in length of the embryo, and it is because 
I also believe so strongly in the importance of the distinction 
that I wish to establish the more accurate terms above. I 
may also claim to have arrived at my conclusion by actual 
experimental observation, having spent mnch time in so 
doing’, and, as evidence of this, I may mention my papers of 
the years 1894, 1896, 1905. 
Hnbrecht hardly does me justice in ignoring my experi- 
inental evidence on the subject. Moreover, this theme was 
the gist of my tliree papers in 1894, “Re-investigation of 
the Early Stages of the Development of the Rabbit,” “ The 
I’l’imitive Streak of the Rabbit,” and “On the Growth in 
Length of the Erog Embryo,” from the last of which I may 
quote one paragraph from p. 288 : “ In other words, I 
believe that as in the rabbit, so in the frog, there is evidence 
to show that the embryo is derived from two definite centres 
of growth, the first, and phylogenetically the older, being a 
protoplasmic activity which gives rise to the anterior end of 
the embryo (= gastrula stage) ; the second, which gives rise 
to the growth in length of the embryo; which centres of 
growth occupy the same relative positions in location and in 
sequence of time, and probably to each are due the same 
parts of the embryo.” 
In my subsequent papers on the chick, 1896, and gi-owth 
centres, 1905, I have described some of a good deal of 
experimental work which I have done in confirmation of this 
opinion. 
Rut although Hubrecht now tpiite agrees that notogenesis 
has nothing whatsoever to do with gastrulation, it is quite 
evident that his conception of notogenesis is not the same as 
mine of deuterogenesis, and since I believe that my conception 
is nearer the truth than his, I must explain where, as it seems 
to me, his error lies. 
In the first place I should like to refer to a footnote which 
appears in Hubrecht’s English edition of his paper, “The 
Gastrulation of Vertebrate.s,” in the ‘Quart. Journ. Micr. 
