ADDENDA 261 



gradient concerned with water-appropriation, analyses its 

 action, and discusses it in relation to other ' axial gradients ' 

 of Planarians (see pp. 171-2'). 



Olmsted and Baumberger (1923) state that in the crabs 

 Hemigrapsus oregenensis, H. nudus, and Pachygrapsus cras- 

 sipes, carapace length increases in a linear relation with 

 carapace width. Unfortunately they do not give their actual 

 measurements, and their graphs, in which individual points 

 are plotted, might equally well indicate slight heterogony. 

 This is especially so with P. crassipes, where length seems to 

 show slight positive heterogony relative to width. In H. 

 nudus the points are too few for any conclusion, and in H. 

 oregonensis the relation appears to show if anything a slight 

 negative heterogony. There must be marked heterogony of 

 the male chela, especially in H. oregonensis, where large males 

 have chelae up to 30 per cent of total weight, while the value 

 for large females is never over 7 per cent. In Carcinus maenas, 

 Huxley and Richards (1931) find a slight heterogony of carapace 

 length. 



Mr. G. H. Locket kindly allows me to cite his results (unpub- 

 lished) on the chelicerae of the spider Theridion lineatum. The 

 jaw undergoes heterogonic growth and takes on its definitive 

 appearance only at the last moult, at which sexual maturity 

 is attained ; prior to this it appears to be almost isogonic. 

 (In the genus Linyphia, there are signs of heterogony at the 

 penultimate moult.) The jaw (basal joint, paturon) of the 

 adult male is much elongated, whereas that of the female 

 remains more nearly similar to that of the juvenile stages. 

 The adult jaw has a prominent tooth on its inner surface, 

 and measurements can be made of the lengths proximal and 

 distal to this. Sternal area was taken as standard body 

 measurement, and the square root of this was used as a stan- 

 dard against which to plot linear jaw measurements. There 

 is a moderate size-range in adult females, a considerable one 

 in adult males (probably dependent mainly on differences in 

 total moult-number). It is clear that in the formation of 

 the male type (i) jaw-breadth and jaw-length are both posi- 

 tively heterogonic, but length much more so than breadth 

 (k = about 1-9 as against about 1-3) ; (ii) in regard to length- 

 growth, the basal region, proximal to the tooth, is roughly 

 isogonic, while the distal region beyond the tooth is very 

 highly heterogonic (k = 27) ; (iii) the length of the falx 

 (distal joint, unguis) is highly heterogonic (k = 2-6), but less 



