BJiEEDlNG-HABITS OF SOME WEST-AERICAN FISHES. 123 



the succeeding pairs as shown in PL X. figs. 10 &U, Eg. i. Here also may be seen, 

 through the dorsal wall, the auditory cavities and the now large fourth ventricle. 



Just before the stage of PI. X. fig. 12 is reached, pigment begins to appear first 

 in the retina, then on the surface of the head. The fin-folds of the tail now begin to 

 grow rapidly, and attain a much greater size than in Lepidosiren {op. cit. figs. 31, 32, & 3.3). 

 A copious network of blood-vessels spreads over the yolk. The sucker is fully functional, 

 and the larvae hang vertically from the sides of the nest or vessel in which they may 

 be confined. Although in Lepidosiren this organ is more conspicuous, yet the larvse 

 appear only to use it for clinging to the uppermost layer of debris in the nest, and so 

 prevent their falling downwards and getting smothered i. 



A striking feature of Protopterus at this stage, compared with Lepidosiren {op. cit. 

 figs. 31, 32), is the serial arrangement of the external gills, their roots being distinct 

 from one another, and placed in a line along the dorsal surface of the deepest part of 

 the yolk. Anterior to the first branchial cleft there is a faint indication of a spiracular 

 cleft between the mandibular and the hyoidean arches (PI. X. fig. 12, sp.) of which in 

 Lepidosiren, externally at least, there is no trace. 



The roots of the external gills in Protoptertis (PI. X. fig. 13) remain longer separated 

 from one another than in the Lepidosiren (op. cit. fig. 33). The three posterior pairs also 

 attain a greater proportionate size. At this stage the tail and dorsal fin-fold are 

 considerably more developed than in the corresponding stage of Tjepidosiren. 



As the external gills are reaching their maximum development, the origin of the 

 gills become somewhat concentrated and rotate forwards, the hindermost gill becoming 

 dorsal, the anterior becoming ventral. 



For some days before leaving the nest, when the young larvce are hanging suspended 

 vertically from its walls by their suckers, the external gills are held stiffly out at right 

 angles to the axis of the body, forming a radiating frill around the base of the head. 

 When the larva is lying in a small trough of water, the gills are not thus erected, and 

 as the drawing (PI. X. fig, 13) was taken from a living specimen, the gills are shoM'n 

 lying back along the sides of the body. 



The pectoral and pelvic limbs develop synchronously as in Lepidosiren, and are just 

 beginning to bud in PI. X. fig. 12, h.l. Correlated with the extension backwards of the 

 roots of the external gills, the position of the bud of the pectoral fin is also far back, 

 and lying immediately below the last external gill, is hidden by them. In PL X. 

 fig. 13 the pectoral limbs are of about the same size as the shafts of the external gills. 

 In one case a specimen had not developed the pinnae of one external gill. This bare 

 shaft so much resembled the pectoral limb, that the larva appeared to have two pectoral 

 limbs on one side. 



In PL X. fig. 13 the operculum is growing back, the mouth is open, and the internal 

 gills functional. The larvae do not breathe air before leaving the nest. There is now a 

 considerable development of pigment, especially in the anterior dorsal part of the 



^ Kerr, loc. cit. p. 316. 



VOL. XVI. — PAUT 11. No. 6. — August, 1901. ' t 



