ADDENDA 259 



of minimum to maximum breadth of head and of gula. The 

 minimum head-breadth is anterior; the maximum gular- 

 breadth is at a spot close to the maximum head-breadth, with 

 maximum gular-breadth more anterior. Accordingly we find 

 these ratios move in opposite directions with increasing 

 absolute size, that for head increasing steadily from below 

 o-6 to over 0-65, that for gula decreasing steadily from over 

 07 almost to 0-5. This means that with increased absolute 

 size, the lateral growth of the head (and its parts) is relatively 

 greater anteriorly than in the region of maximum width. 

 And this, we may presume, is correlated with a relative 

 increase of jaw-size, though Light gives no data on this point. 



With reference to the conclusions of Hecht (p. 38), the 

 work of Keys (1928) also indicates that Hecht's assumption 

 of form-constancy in teleost fish is not strictly true. He finds 

 that in herrings, sardines, and Fundulus the weight increases 

 faster than the cube of the length, which implies form-change. 

 Somewhat similar results have been obtained by Hickling 

 (1930) for the dogfish Acanthias vulgaris. 1 



In connexion with the law of antero-posterior development, 

 and the graded changes it may induce (see p. 132), the follow- 

 ing point, which has been brought to my notice by Professor 

 R. J. S. McDowall, is of interest. Bray (1931) finds that the 

 incidence of eczema on different regions of the body varies 

 with age. The incidence for head and neck declines with 

 age, that for extremities increases with age, while that for 

 the trunk remains approximately constant. There is reason 

 to believe that the incidence of ringworm behaves in a some- 

 what similar way. 



Gajewski (1922) discusses the effect of salinity upon Artemia 

 salina, whose form-changes continue long after sexual maturity. 

 Increasing salinity diminishes final absolute size, and also 

 changes bodily proportions, as seen in the following table (for 

 females : males are similar). 



Salinity (Baumez). . 4 f 12 18 2 2° Be 



Body-length, mm.. . 15-56 I 3'°5 IO '65 9-62 7-8 



Post-abdomen 



— — ; ratio . o-Q2 1-02 1-20 1-30 1-42 



abdomen 



Length-breadth ratios : 



Of 8th post-abdominal 



segment . .2-3 27 3-5 4-5 5-0 



Of 7th ditto . . 1-3 1-35 1-4 1-5 i-6 



Of gill-sacs of 6th foot . 2-0 1-9 i-8 1-7 



1 The same is indicated for the Bittering, Paracheilognathus, by the 

 data of Shaw (1931), Bull. Fan. Memor. Inst. Biol., 2, 245. 



17* 



