262 PROBLEMS OF RELATIVE GROWTH 



so than the distal region of the main jaw. Here we find 

 differential growth operative definitely within a single segment 

 of an appendage (compare pp. 81, 98). 



In the female, the figures are more irregular, but jaw-area 

 and falx-length clearly show negative heterogony, while the 

 distal region of the jaw is distinctly positive. Jaw-length as 

 a whole is approximately isogonic, which means that jaw- 

 breadth must be negatively heterogonic. 



In the spider Dolomedes plantarius, P. Bonnet (La Mue, 

 L'Autotomie et la Regeneration chez les Araignees, These, 

 Toulouse, 1930) in his Table 25 gives measurements of the 

 lengths of legs at all instars from 2nd to nth (adult) in two 

 individuals. From these the mean increases per moult can 

 be calculated ; and it is then found that all the legs are in- 

 creasing at the same rate — i.e. for this region of the body 

 there exists no growth-gradient comparable to that seen in 

 hermit-crabs, etc. (p. in). 



W. Beebe (Tropical Wild Life in British Guiana, 1917, 

 chaps. 18 and 19) gives some data as to the heterogony of 

 the claws of the Jacana. That of the hind toe is greatest. 

 In the embryo the claws are not dissimilar to those of other 

 birds and the hind claw-length is about ^ of the toe-length ; 

 in half-grown chicks it is \, in adults about f. 



The other claws grow more slowly, reaching about § of the 

 length of the hind-claw ; their relative breadth-growth is greater 

 than that of the hind-claw. The heterogony of the claws begins 

 only in the late embryo ; that of the toes begins much earlier. 



He also refers to the bill of the aberrant cuckoo-like Ani, 

 which is swollen in the adult. It, however does not begin 

 its positive heterogony until after the young bird has left the 

 nest. At hatching, it is typically cuckoo-like, though some- 

 what swollen. It would be interesting to obtain accurate 

 measurements on these structures. The case of the Jacana is 

 interesting, since the great length of toes and claws is quite defin- 

 itely adaptive, allowing the bird to walk over floating leaves. 



G. Duncker (1903 ; Biometrika, 2, 307) attacks the problems 

 of growth-correlation and asymmetry in male fiddler-crabs 

 (see pp. 80 and 121) by means of standard biometrical 

 methods. These, however, failed to give any very important 

 biological information, e.g. as to growth-centres or growth- 

 gradients, or at least nothing so clear-cut as is to be obtained 

 by the simple methods of taking means for a number of size- 

 classes. The growth-gradient in the large chela is indicated 



