34 PROBLEMS OF RELATIVE GROWTH 



relative growth of homologous organs next shows that 

 the same organ may behave very differently, as regards 

 its growth-behaviour, in different forms. For instance, the 

 chela of male Uca pugnax shows heterogony on one side 

 of the body only, but shows it throughout all but the first 

 instar of post-larval life, with a decrease in its growth-coefficient 

 apparently at the time of sexual maturity. In the spider- 

 crab Maia squinado (Huxley, 1927 ; and unpublished), both 

 chelae are heterogonic, but heterogony does not set in until 

 quite late in life, presumably at sexual maturity, and then 

 continues till death. The same appears to be the case with the 

 large prawn Palaemon carcinus (Tazelaar, 1930), though here 

 the chelipeds are the second and not the first pereiopods ; 

 and with the spider-crabs of the genus Inachus. But in the 

 latter the male chelae revert more or less completely to the 

 female type in the non-breeding season ; this reversion is 

 much less marked in I. dorsettensis (Shaw, 1928) than in 

 7. mauritanicus (Smith, 1906A). In various other crabs, and in 

 lobsters, crayfish and pistol-crabs (Alpheus), both chelae are 

 heterogonic, but with different growth-coefficients, leading to 

 the condition of heterochely. Furthermore, the sex-difference 

 as regards the growth-coefficient of the chela may vary, some 

 forms having equal positive heterogony in both sexes, others 

 showing positive heterogony in both sexes, but with a lower 

 growth-coefficient in the female, and still others showing male 

 heterogony but female isogony. This variability is particu- 

 larly well shown in prawns (Palaemonidae) ; in these, further, 

 the large chela is the second, not the first pereiopod. Finally 

 in Gammarus chevreuxi, Kunkel and Robertson (1928) have 

 shown that the marked heterogony of the male gnathopod 

 begins shortly before sexual maturity and ends shortly after, 

 its growth being roughly isogonic for the much longer previous 

 and subsequent periods. (Cf. also birds' wings, p. 263.) 



A similar state of affairs is seen in regard to the abdomen 

 of female Brachyura. This must always be heterogonic for 

 some part of its development, since it is always broad in the 

 adult, always narrow and of male type in the young juvenile. 

 A state of affairs similar to that of the large male chela of Uca is 

 found in the female abdomen of Carcinus maenas — it is hetero- 

 gonic (with a late increase in intensity) from the earliest stages 

 until the end of life. The details for both sexes at all ages are 

 shown and described in Fig. 7. In female Uca, on the other 

 hand, while heterogony is initiated at the beginning of post- 



