6i6 SCIENCE PROGRESS 



phibian metamorphosis, but certainly less well analysed, and 

 almost certainly more complex. Different glands are deve- 

 loping at a different rate relative to each other and to the body 

 as a whole ; each may vary independently of the rest, and the 

 end-result may be accelerated or retarded accordingly. In 

 some rare cases we get a state of affairs essentially comparable, 

 as a process, to neoteny — we get delay in differentiation pushed 

 to such a pitch that maturity never occurs at all. 



In the Loraine type of infantilism, the pituitary appears 

 to be underdeveloped ; but, whatever be the cause, full sex- 

 differentiation remains absent for a number of years after 

 the normal date of puberty. Ateleotic dwarfs are infantile in 

 another way. They are not merely of small but of diminutive 

 stature ; the body as a whole is in many respects extremely 

 infantile, while the sexual organs often mature with compara- 

 tively small delay. In other cases, however, the delay is 

 considerable, while in one subtype maturity never occurs. 

 This gradation from normal time-relation through delay to 

 non-appearance is of great interest, as it indicates that 

 there are steps in the process, that it is a case of originally 

 balanced equilibrium tilted right over to one side, exactly as 

 in neoteny (7, 9). 



Finally we should mention the extraordinary but happily 

 very rare phenomenon known since Hastings Gilford's work 

 (9, 10) as progeria. In these cases, superimposed on an attempt 

 at normal development, there is a precocious senilit}'' producing, 

 if not a " gre3^beard of five," as in the Bab Ballads, at least a 

 miniature very old man in under twenty years. Part of the 

 mechanism which runs the body is out of gear, and is, it would 

 seem, causing the cycle to be run through at excessive speed. 

 In connection with this, we should remember that the cycle 

 in different species does run at different rates. In the rat or 

 mouse, for instance, the embryo at a given size is far more 

 differentiated than a human embryo of the same age, and the 

 phases of the cycle — infancy, adolescence, maturity, and old 

 age — are flashed through at an increased tempo. 



Undoubtedly, similar but much smaller differences in 

 general tempo can exist in individuals or races of the same 

 species, and these will probably give curious phenomena on 

 crossing. Goldschmidt's intersexes in moths appear to owe 

 their production to some such general differences in rates of 

 differentiation. It is no use investigating only their qualita- 

 tive effects. Various lines of evidence indicate — what the 

 study of amphibian metamorphosis has shown definitely to be 

 true in certain cases — that many of the ductless glands are 

 true regulators, in that they simply modify the rate of pro- 

 cesses which would take place anyhow. Mammalian meta- 



