128 PROBLEMS OF RELATIVE GROWTH 



their rate of regeneration is greater when both are on one 

 side of the body than when they are on opposite sides ; and 

 the same holds good when three different legs are removed. The 

 mean difference amounts to nearly 5 per cent, of the lower figure. 



Further, if two legs are removed, regeneration of a given 

 leg is greater (by nearly 3-5 per cent.) if the other leg is the 

 opposite member of the same pair than if it is a leg of another 

 pair, whether on the same or the opposite side. On the other 

 hand, when only one leg of a pair was amputated, its normal 

 partner on the opposite side was not accelerated in growth, 

 but if anything slightly retarded (mean, 0-4 per cent, retarda- 

 tion — a figure which may however well fall within the limits 

 of experimental error). This result cannot be compared 

 directly with the corresponding results in Przibram's Sphodro- 

 mantis, since it only concerns growth during one instar. 



Going through his tables, however, I have come across one 

 fact which appears to be significant for our problem. When 

 legs belonging either to two or three different segments were 

 amputated, whether on the same or opposite sides, the amount 

 of their regeneration can be compared with the amount made 

 by the same legs when only a single leg is amputated. It is 

 then found that the anterior of the regenerating legs always 

 regenerates relatively less rapidly than the posterior (only one 

 exceptional result in eight series of experiments) ; in five out 

 of the seven concordant series, the regeneration of the anterior 

 limb is actually below the ' normal ' amount for regeneration 

 of the corresponding single limb, and that of the posterior 

 limb equal to or greater than normal. This again points to 

 a depressant effect of rapid growth on anterior structures, 

 and a stimulative effect on posterior ones. 



It will, however, be necessary to carry out systematic experi- 

 ments, using repeated regeneration, before clear-cut results 

 can be obtained. 



§ 5. Some Cases of Teratological and Abnormal Growth 



In this connexion, the measurements made by Nanagas 

 (1925) on human anencephalic foetuses are of interest. In such 

 monsters, the size and proportions of the trunk and especially 

 of the lower limbs, are practically normal, but, while the cranial 

 region is, of course, markedly underdeveloped, the fore-limbs 

 are hypertrophied (by about 12 per cent.). Furthermore, the 

 hypertrophy is graded (Nanagas' Table I) : the upper arm 

 shows an increase over the normal of 24 per cent., the fore- 



