744 LIFE : OUTLINES OF GENERAL BIOLOGY 



experiment is enough in itself to show that the blindness of certain 

 cave fishes need not necessarily be ascribed to the darkness; it 

 might readily arise in response to some penetrating environmental 

 change, such as low temperature. (/) If the developing eggs of the 

 same fish (Fundulus) are subjected to various reagents, such as 

 butyric acid, there result numerous strange monstrosities in eyes 

 and ears, nostrils and mouth, even in heart and fins. The chemical 

 intrusion seems to dislocate and partially dissolve the germinal 

 material, especially towards the head end. This may throw some 

 light on monstrosities, for butyric acid derivatives appear in higher 

 animals as the result of some disturbance in the carbohydrate 

 metabolism, and a consequent poisoning of the mammalian mother's 

 constitution might result in monstrosities in the early embryo. On 

 a similar but very different line, some interesting light has been 

 thrown on the development of galls in plants; the tissues react in 

 a specific way to the salivary secretion of the larva of the gall-fly. 

 {g) If the larva of the blind newt Proteus be reared in the laboratory 

 under red light, the eye, which is normally arrested in the darkness 

 of the caves, increases in size, reaches the surface, and may continue 

 its development to the extent of becoming a seeing eye. The reason 

 for the red light is that in white light the skin becomes darkly 

 pigmented, which shuts off the stimulus from the developing eye, 

 so that its differentiation is not continued, (h) According to Baltzer's 

 account of the development of the green worm Bonellia, notable for 

 its extraordinary sex dimorphism, those free-swimming larvae that 

 settle down on the floor of the sea develop into large green females 

 with a body an inch or two in length and a flexible food-capturing 

 proboscis which may be a foot long. But those that settle down on 

 the proboscis of a full-grown female and begin to absorb the skin- 

 secretion have their development inhibited, and become pigmy 

 males. Those larvae that Baltzer helped to attach themselves to the 

 proboscis of a full-grown female, but left attached for a very short 

 time, subsequently developed into almost perfect females. Those 

 that he left attached for a long time became the ordinary pigmy 

 males, with unrecognisably simplified structure, which live parasiti- 

 cally in the female. But those that Baltzer left for intermediate 

 intervals of time showed various stages of inter-sex. Goldschmidt's 

 criticisms have to be considered, but the main facts seem to be 

 secure. 



There is more than verbal progress in the recognition that em- 

 bryology cannot be limited to the study of the young animal. 

 It is plain that the larval stages must also be included, and the 

 difficult phenomena of metamorphosis. But one cannot logically 

 exclude such strange dis-organisations and re-differentiations as are 

 involved, for instance, in the "brown body" of many Polyzoa or in 

 the seasonal relapse and rejuvenescence of some Tunicates. The 



