High and low Dimorpliism. 327 



Para tana is Batet 



Now we bave seen tliat within the speeies L. diibia^ hig-h aud 

 low males occur which differ from one auother iu two of the 

 cliaracters imder cousideration, uamely the chela and the antenna; 

 while the uvopod having its two branches equali zed is intelligible 

 on the hypotbesis tbat the smaller speeies bave been split off at a 

 so to speak larvai stage in the growtb of the larger forms. 



The coincidence tben of tbis high and low dimorpbism within 

 the speeies with the existence of high and low speeies in a compact 

 group appears to me to point to the principle of high and low 

 dimorpbism as an important factor in their evolution. For besides 

 their size and the characters which concern the secondary sexual 

 characters and the uropod, the different speeies of tbis group are 

 practically indistinguisbable. There is one other fact which seems 

 to me to show tbat tbese speeies are to be regarded as races which 

 bave been split up partly owing to changes in the stage of growth 

 at which maturity is reached. And tbis is tbat the females of the 

 smaller speeies appear to breed mach faster and take less time in 

 becoming mature than the larger forms, and tbis is the more marked 

 the smaller the speeies is. Tbus one finds more than half the females 

 of P. Batei at ali times of the year with cggs, but only a small 

 percentage, perbaps 10^ o of -^- dubia. Tbis appears to me to be of 

 signiticance. 



We must now look for parallel facts in the Lamellicornia. 



B. Lamellicornia. It is impossible to maintain tbat the prin- 

 ciple of high and low dimorpbism is the sole factor in the evolution 

 of the groups considered; we may go further and say tbat it is 

 e([ually impossible to claim tbat the differentiation of the secondary 

 sexual characters is solely due to tbis principle. Mr. Arrow, of the 

 British Museum, to wbose courtesy I am mach indebted, pointed 



Mittheilungen a. d. Zoo!. Station zu Neapel. Bd. 17. 22 



