6o8 ON INCREASE IN COMPLEXITY [pt. iii 



nervous tissue went on proliferating for nearly a week. In such 

 embryos the mesenchyme cells seemed almost unaffected by the 

 suffocation, and continued to divide, but took on the histological 

 characteristics of blood-cells. The important point about the picture 

 in anaerobic embryos was that each cell became a relatively free 

 unit, and all correlation of growth as well as all further differentiation 

 ceased with the circulation. Only unorganised cell-life was possible. 



No consideration of organisation in growth could omit the subject 

 of mitogenetic rays, from which it appears that radiant energy of 

 definite wave-length is given off by cells in mitosis as an excitant 

 to adjoining cells not in mitosis. For detailed information on 

 this subject, the book of Gurwitsch & Gurwitsch and the memoir 

 of Borodin should be referred to. Genuine uncertainty still exists, 

 however, about these rays, and a whole literature is growing up, 

 partly consisting of reports of workers who confirm Gurwitsch's 

 results, and partly of the reports of those who do not. 



Anikin has already attempted to relate the activity of these 

 " mitogenetische Strahlen" to organiser phenomena, and Sorin & 

 Kisljak-Statkewitch have examined all the parts of the hen's egg, 

 using onion roots as detectors for the rays. Negative results were 

 obtained with albumen from the 2nd day of development, the vegetal 

 pole of the yolk throughout incubation, the white and yolk of in- 

 fertile eggs, even if incubated, the "Brei" of germinal spots 36 hours 

 old, cerebro-spinal fluid and brain tissue from 5-day embryos, the 

 amniotic liquid and certain other parts. On the other hand, positive 

 results were always obtained with the substance immediately under 

 the germinal spot up to the 6th day of development and with the 

 blood. Karpass & Lanschina also find peptic and tryptic digests of 

 egg-yolk to be powerful sources of mitogenetic rays. 



3-10. Chemical Embryology and Genetics 



The relations between physiological and chemical embryology and 

 genetics, on the other hand, afford a more solid basis for discussion. 

 It has frequently been found that the behaviour of organisms of 

 known genetic constitution during their embryonic period affords a 

 means of marking out the points in ontogenesis at which genetic 

 factors come into play*. The simplest case of this kind is the question 



* Some embryological factors seem to be determined entirely by the maternal organism 

 (Toyama for pigmentation of silkworm eggs, Diver, Boycott & Garstang for dextrality 

 and sinistrality of Limnaea eggs) . 



