86 Records of the Indian Museum. [VOL. X, 



at variance with the results obtained by Borradaile and for this 

 I am unable to offer any adequate explanation. 



Judging from the Indian examples the variation in the males 

 of Saron marmoratus is closely similar to that found in certain 

 freshwater prawns of the family Palaemonidae. In a number of 

 species of this family the second peraeopods of some males are 

 found to have attained a huge size, while in other individuals of 

 the same sex and species they resemble those of the female: if 

 sufficiently large numbers are examined it is found that the speci- 

 mens fall into a more or less well-graded series and that it is 

 impossible to separate them into two or more groups. Coutiere 

 considers that dimorphism also occurs in the Palaemonidae ; but 

 his detailed study of its occurrence in Palaemon {Eupalaemon) lar,^ 

 although of great interest, does not convince me that this is the 

 case.* 



Smith defines high and low dimorphism in the following 

 terms'*: — "It consists essentially in the existence among the 

 males of an}- species of a graduated series, as regards size and the 

 development of the secondary sexual characters, such that the 

 smaller males have relatively poorly developed secondary sexual 

 characters while the larger males attain to a much greater relative 

 development of those characters. The smaller males are then 

 termed ' low,' and the larger males "high": when there is a more 

 or less abrupt transition in point of numbers from high to low 

 males we may most properly speak of a high and low dimorphism 

 existing in the males of that species, but we also apply the term 

 more loosely to those cases in which no such abrupt transition is 

 proved to occur." 



If the last sentence in this paragraph be accepted, the pheno- 

 mena found in these Caridea may correctly be described as dimor- 

 phism, but to do so would, in my opinion, only tend to obscure 

 the real nature of the case. In Saron, Palaemon, and certain 

 other genera it appears that the male may become sexually mature 

 at a period when, in its secondary sexual characters, it shows but 

 little external difference from the female; but that it gradually 

 assumes the more striking features of its sex in the course of 

 subsequent moults, just as the male parr in which the milt may 

 be ripe gradually assumes the appearance of the adult milt 

 salmon. In Caridea, therefore, the case is one of gradual transi- 

 tion rather than of true dimorphism, by which is implied either a 



^ Coutiere, Ann. .Sci. nat. Zool. (8), XII, p. 292 (1901 ). 



Henderson and Matlhai in their account of the freshwater Palaemonidae of 



Southern India (Rec. Ind. Mus., V, 1910, p. 280) have advanced certain facts 



vvhich seem 10 mdicate that Palaemon scabn'ciilits, P. dolichodactvl us and 



P. diibius, belong in reaHty to a single species. This suggestion is a most 



'"•'i?'k'"^'"^ "'-"^ '^'^'^' '^'^ ^^ ^^ proved, trimorphism in the males of Palaemonidae 

 will be eslablished. The case, however, is on an entirely different footing from 

 that cited above, for the three forms, all founded on niales of large size, dift'er 

 from one another in well-marked characters drawn from the proportional lengths 

 of the individual segments of the second peraeopods. 



3 Smith, Mitth. zool. Stat. Neapel, X\TI, p. y2 [U)(M. 



