124 M]{. .r. S. BUIJGETT ON THE 



body. The fin-rays arc just making their appearance in the fin-folds of the tail. The 

 sucker or cement-organ is at its maximum development. The tail is absolutely dipliy- 

 cercal from the first. IJlood-vessels running in the track of the spiral valve shine 

 through the body-wall (PI. X. fig. 12, s.v.g.). The spiral valve is lirst indicated in fig. 12. 

 The yolk remains chiefly massed in the original position close behind the sucker, and 

 is not distributed along the gut to the same extent as in Lejndosireu {op. cit. figs. 3o, 

 34, & 35). Wherever yolk is seen, it is of the original greenish colour. 



The young Protopterus leaves the nest with practically the form of the adult 

 (PL XI. fig. 3). The mass of food-yolk is not entirely absorbed as yet. The first pair 

 of external gills has been lost, and the succeeding pairs have been much reduced in 

 size. The tail ends in a very fine filament. The markings of the young Protopterus 

 at this time are somewhat different from the adult. The general colour is dark brown, 

 a conspicuous broad yellow band passing between the eyes. As with Lepidosiren so 

 with Protopterus, the larvae at this stage contract their black chromatophores at 

 night and become blood-red, the eye shining out deep black in contrast. 



It is here interesting to notice that the larval Protopteri, after leaving the nest when 

 kept in an aquarium the bottom of which was covered with seedling water-lilies, 

 chara, &c., never show themselves by day, and if disturbed from their seclusion, hastily 

 make their way back to their hiding-place. After dark, however, by the aid of a 

 lantern, the larvte may be seen swimming around in the most lively manner, but they 

 do not come to the surface for air. 



It seems, then, that the habit of expanding the chromatophores by day is of advantage 

 to the larval Protopterus, making it almost invisible while lying passively on the dark 

 soil. The chromatophores become contracted by night, not by reason of the darkness, 

 but because this is the period of activity with the larvee, and when swimming about 

 they are certainly less conspicuous when transparent than when opaque, even at night. 



Were it customary for the larval Protopterus to swim about in the daytime, they 

 would probably then contract their chromatophores, becoming less visible with 

 increased transparency. As a matter of fact, when in the daylight the larvae were 

 placed in a white porcelain dish, in a large number of cases they did contract 

 their chromatophores. That this contraction on a light background did not always 

 take place may possibly be accounted for by supposing that continued habit has 

 produced a certain periodicity in the contraction and expansion of the chromatophores. 



While on the Gambia, I kept a large number of young fry of about fifteen species of 

 fishes, and I noticed that the nocturnal forms did become more transparent at night. The 

 converse was naturally not noticed, since I know of no fishes which are only active in 

 the daytime. AVith frogs, the case is quite different, for they are not aquatic, and would 

 not therefore be made less conspicuous by being transparent. The chromatophores 

 are often contracted by them in the daytime when exposed to strong sunlight, for the 

 objects around them then become of brighter and lighter colour ^ 



• "Notes on the Batrachians of the Paraguayan Chaco," Q. J. M. S. 1S99, pjj. 314, 327, 328. 



