978 



MR. C. TATE REOAX OX 



limnophagous structure has been evolved three or four times 

 independently. 



The intromittent organ is freely movable and is supported 

 internally by bony stays, 2 to 5 in number, that project down- 

 wa,rds and forwards from the bridges that connect the parapo- 

 physes of the posterior praecaudal vertebrae. It is formed by the 

 prolongation of the tlurd, fourth, and fifth anal rays, the first 

 and last of which are stout and are more or less expanded trans- ' 

 versely so as to mai'gin a groove on one side or the other, or they 

 may even meet so as to form a tube. The ui-ogenital orifice is 

 directly in front of the base of the fin, and may often be covered 

 by the pelvic fins, which, doubtless, help to conduct the seminal 

 fluid into the groove, or in certain forms where the pelvic fins of 

 the male are considerably enlarged they may be closely applied 

 to the intromittent organ, converting the grooves into closed 

 tubes. The distal segments of the prolonged rays may be 

 variously modified into spines, hooks, barbs, etc., which may help 

 to retain the organ in position during coition. 



The differences in structure of the intromittent organ are of 

 great systematic importance ; hitherto they have been almost 

 neglected, except by Eigenmann (Proc. U.S. Nat. Mus. xxxii. 

 1907, p. 425), who has described them in the genera Lehisies, 

 Girardinus. Glaridichthys, Phalloceros, and Phalloptychxis *. 



Many of the species eat Mosquito larvae, and the " Millions " 

 fish {Lebistes reticidatus) has been introduced into many countries 

 in the hope that it will check malarial fever f. On account of 

 their small size, pretty appearance, and interesting habits the 

 Pceciliinse are great favourites with European aquarium -lovers, 

 especially in Germany ; several of the new species described 

 below have been sent to me by my valued cori'espondents in 

 Hamburg, Herr J. P. Arnold and Herr A. Rachow, as newly 

 imported aquarium-fishes. In the Gei-man aquarium-journals 

 and in two booklets by Stansch (Die lebendgebarende Zahnfarkfen, 

 Leipzig, Wenzel, 1910, 1911) have appeared many accounts of the 

 habits of different species : from these one gathers that the 

 broods follow each other at intervals of only a few weeks, but 

 that the number of young varies greatly according to the species ; 

 thus a pair of Pcecilia parce had broods of 8, 11, and 10 at 

 intervals of four weeks, but in P. vivipara 124 were counted in a 

 single brood. The new-born young are usually from 5 to 10 mm. 

 long and grow rapidly, in many species attaining sexual maturity 

 in about three months. The breeding-habits are of great interest : 

 in species where the males are brilliantly ornamented {Mol- 

 lienisia, Xiphophorus, Poecilia hranneri) they dart about displaying 

 their beauty ; in these and in related forms the females appear 

 to encourage their advances, but in others they are quite shy 

 and their mates have to exercise cunning to get near them. It 



* Some additional iiguves are given by Lang-ev in a paper on tlie morpliology of 

 these fishes, just publislied (Morph. Jalirh. xlvii.). 

 t See P. Z.S. 1911), p. 116; 1012. p. 900. 



