260 PROBLEMS OF RELATIVE GROWTH 



The furca diminishes disproportionately with increasing 

 salinity. It would be of great interest to investigate the 

 growth-coefficients of various parts accurately in different 

 salinities. This is an important addition to Chap. VI, § 7. 



Murr (1929) x gives particulars concerning the relation 

 between retinal cells and the body as a whole in various 

 mammals, both as regards relative size, and relative develop- 

 mental rate. The results are interesting both as regards 

 individual ontogeny and comparative physiology. 



Unpublished work which E. B. Ford kindly allows me to 

 quote, on relative eye-size in males of the red no-white mutant 

 of Gammarus chevreuxi at 23 C, shows that after a head- 

 length of a little over 0-5 mm. has been attained, up to the 

 maximum size (head-length 1-64 mm.) there is simple negative 

 heterogony both of eye-length (dorso-ventral) and eye-breadth 

 (antero-posterior) against head-length (antero-posterior), the 

 growth-coefficients (k) being 0-89 and 071 respectively. 

 Immediately after extrusion, however (head-length 0-25 — 0-3 

 mm.), both dimensions show positive heterogony (k nearly 

 2 -5 for eye-length and over 1-5 for eye-breadth), subsequently 

 diminishing regularly to reach their definitive values. As 

 consequence eye-breadth relative to eye-length shows a steady 

 negative heterogony with k a little below o-8 during the 

 ' definite ' period and for a little before it, with a still lower 

 k value (o-6 to 0-65) for the earliest stages. The early phase 

 of positive eye-heterogony would seem to be due to the late 

 development of the organ, which is not fully differentiated 

 at the time of extrusion. (See Chap. IV, § 7.) 



With reference to the correlation between growth-rate 

 and sensitivity to female hormone in fowl feathers (p. 101), 

 Lillie and Juhn (1931) find that this holds also in different 

 parts of the single feather. This growth-gradient has im- 

 portant consequences for the development of certain feather- 

 patterns. 



With reference to bio-electric phenomena (p. 174), Purdy 

 and Sheard (1931) find in human beings that there is a definite 

 association of ' low metabolism with large differences of 

 electrical potential as measured at the extremities of the 

 body ' and vice versa. 



J. W. Buchanan (1930, J. Exper. Zool., 57, 307 and 455) 

 establishes the existence of an antero-posterior osmotic 



1 Murr, E. (1929), Zur Entwicklungsphysiologie des Auges, II, 

 Biol. Zentralbl., 49, 346. 



