ZOOLOGY AND BOTANY", MICROSCOPY, ETC. 573 



c. General. 



Evolution Theory in the Light of Genetics.*— C. B. Davenport 

 discusses "the form of evolutionary theory that modern genetical 

 research seems to favour." His conclusion is that "a theory of 

 evolution that assumes internal chancres chiefly independent of external 

 conditions, i.e. spontaneously arising, and which proceeds chiefly by a 

 splitting up of and loss of genes from a primitively complex molecular 

 condition of the germ plasm seems best to meet the present state of our 

 knowledge." 



Such a theory receives support from various fields : — (1) From 

 ontogeny, where the differentiated end stage is derived from a relatively 

 undifferentiated, but probably molecularly complex egg ; (2) from 

 palaeontology, where the history of the phylum seems to be governed 

 by internal laws ; (3) from experimental breeding, where progress is 

 afforded only as internal changes permit ; and (4) from analogy with 

 evolution in the inorganic world, so far as may be inferred from studies 

 on the " rare earths." 



" Such a theory makes clear that success in ' selection ' depends on 

 rate and amplitude of internal change and ability to judge of germinal 

 from somatic conditions. It renders less hopeful (but not hopeless) 

 the prospect of being able to control completely by experimental 

 methods evolutionary change." 



Pineal Gland and Pigmentation.!— Carey Pratt McCord and 

 Floyd P. Allen have studied the influence of pineal gland substance 

 upon pigmentation in tadpoles. It has been suggested that the changes 

 in pigmentation exhibited by blinded animals when placed in new 

 environment may be due to some ocular function exerted by the pineal 

 body. Laurens has shown that this is very unlikely. But the authors' 

 experiments, while not supporting the view that the pineal body may 

 act in the role of its ancient ocular function, show that it contains 

 within itself an active principle capable of inducing pigment changes 

 independent of and wholly apart from environmental conditions. Indeed 

 the changes in pigmentation induced by pineal feeding appear in spite 

 of environmental conditions tending towards the opposite phase. 



Up to near the tenth day of larval life in tadpoles, pigmentation is 

 not influenced by pineal feeding, which may be due to incomplete 

 development of the innervation involved. 



From about the tenth day until near the termination of meta- 

 morphosis, the addition of traces as small as 1 part acetone extract in 

 100,000 parts water determines distinct cyclic pigment changes. Tiie 

 pineal feeding is rapidly followed by loss of colour. Within thirty 

 minutes all macroscopic pigment is lost. The condition is transient, 

 and there is restoration of colour within three to six hours, imless 

 further pineal food is added. As metamorphosis is completed the 

 pigment is no longer altered by pineal materials. 



* Amer. Nat., I. (1916) pp. 449-65. 



t Journ. Exper. Zool. , xxii. (1917) pp. 207-24 (7 figs.). 



