158 



SCmNGE. 



[N. S. Vol. VII. No. 163. 



pletely separated, as perfectly as those of 

 the echinoderm, but in the ctenophor the 

 isolated blastomere develops into a half- 

 embryo. Evidently, then, any new theory 

 of .development must explain how in one 

 case it is possible for an isolated blasto- 

 mere to develop into a half-embryo, and 

 how in another case into a whole embryo. 

 Perhaps the explanation is not far to seek, 

 for it has been found that in one and the 

 same egg the blastomere may under certain 

 conditions give rise to a half embryo, and 

 under other conditions to a whole embryo of 

 half size. 



I might, had I time, cite many other 

 experiments : those, for instance, in which 

 a part of the unsegmented egg has been 

 removed; Boveri's experiment in which 

 a non-nucleated piece of an egg is entered 

 by a single spermatozoon and an embryo 

 forms ; the experiments and observations of 

 the direction of the nuclear spindle in the 

 dividing cell ; the experiments on the effects 

 of different salts on development ; the ef- 

 fects of light, heat and electricity on the 

 egg or embryo, etc. 



These experimental studies will serve as 

 examples of the kind of work of the new 

 embryology. 



The two instances that I have already 

 given — the effect of gravitj' of the egg, and 

 the behavior of isolated blastomeres — teach 

 us that the greatest precaution must be 

 used before we can know whether a sug- 

 gested mechanical explanation is really a 

 true explanation. There is, I think, but 

 one way in which we may hope to find out 

 what forces or energies are at work during 

 development, and whether these forces are 

 the same forces known to the chemist and 

 physicist. Only by means of well-planned 

 experiments can we expect by isolation 

 and recombination to discover the forces 

 at work. Here, it seems to me, we find at 

 least the real meaning and strength of de- 

 velopmental mechanics. 



I admit freely that developmental me- 

 chanics is not a fortunate expression, but, 

 nevertheless, Roux and his school have from 

 the start encouraged experimental methods. 



Perhaps it would be more appropriate to 

 call the new work 'experimental physiology' 

 of the embryo, using physiology in a wider 

 sense than that usually given to it. For 

 myself, I think our aim is reached if we 

 use the term experimental embryology. 



The history of science teaches us that by 

 means of experiment chemistry and physics 

 have made enormous progress ; by means of 

 experiment animal and plant physiology 

 have become more exact, more profound 

 studies than animal and plant morphology, 

 and the department of bacteriology shows 

 how rapidly and surely a study may ad- 

 vance by this method. Therefore, by means 

 of experiment the student of the new em- 

 bryology hopes to place the study of embry- 

 ology on a more scientific basis. 



Morphogenesis. Dk. Chas. B. Davenpoet, 



Harvard University. 



Morphogenesis may be defined as the 

 study which attempts to explain the de- 

 velopment of the form of the individual 

 (ontogenesis) and of the race (phylogene- 

 sis). 



Morphogenesis is a subdivision of general 

 physiology, inasmuch as it deals with activi- 

 ties—processes, and, indeed, the largest, 

 most complex biological processes, those by 

 which the course of individual development 

 is controlled and the direction of evolution 

 is determined. Morphogenesis includes 

 developmental mechanics in so far as that 

 study attempts to explain the ontogenetic 

 processes. 



The scope of morphogenesis, embracing, 

 as it does both ontogenetic and phylogenetic 

 processes, is a broad one. Too broad, some 

 may say who believe that there is no close 

 relation between phylogeny and ontogeny ; 

 that ontogeny goes its way and phylogeny 



