VII. 



Experimental Embryology.' 



EXPERIMENTAL Embryology is the youngest department of 

 biological science ; for although the idea of artificially in- 

 fluencing the germ is very old, and although even Swammerdam 

 is said to have experimented in producing monstrosities, all the 

 important results are very recent. They are already so important, 

 both in themselves and in their suggestiveness, that it is imperative 

 on every biologist to take stock of them. In part this has been already 

 done by Weismann in his recent book on "The Germ Plasm," and 

 by Roux, in an address delivered to the congress of the Anatomische 

 Gesellschaft, held last June in Vienna ; but already there are further 

 researches of moment to be taken account of, and a fresh survey may 

 be permitted. A critical review I do not propose to attempt, partly 

 because that may be more profitably left to the expert embryologists, 

 partly because it may be conveniently deferred until the body of facts 

 has had time to become integrated. 



I. Just as pathology sheds light on physiology — for instance, in the 

 case of the thyroid gland — so teratology may help us to understand 

 normal development. The most successful worker along this line 

 has been M. Camille Dareste. He is the acknowledged chief of 

 artificial teratologists. To attempt an appreciation of his results 

 would lead us far into morphological questions ; ^uffice it to say that 

 he has experimented with the eggs of birds, placing them vertically 

 instead of horizontally, hermetically varnishing part of the shell, 

 keeping them slightly above or slightly below the normal temperature 

 of incubation, heating different parts of the egg unequally, and so on. 

 He has not only shown that the germ is plastic in the grip of its 

 environment, he has been able to induce various malformations 

 which are of interest to the student of morphology. 



Dr. Bertram C. A. Windle, Professor of Anatomy in the Queen's 

 College, Birmingham, has followed up some of Dareste's investiga- 

 tions, observing on the eggs of the fowl the effect of [a) excluding 

 part of the air supply by varnish, [b) incubating under electrical 

 current, and [c) incubating in the proximity of magnets. He is very 

 cautious in his conclusions. He confirms, however, the view of 

 Dareste that the same anomalies may be produced by diverse 



1 A Paper read before the Scottish Microscopical Society, March lo, 1893. 



