DEVELOPEMENT OF BATEACHIA. 625 



The embryonal cells that lay the foundation of these glands, 

 fig, 434, e, are situated in the angle between the intestinal yolk- 

 mass, ib. b, and the stomach, ib. c ; not behind it, as in Fishes, 

 fig. 435. They form a hollow gland or cascum with a wall of com- 

 pacted cells ; and, after a communication has been established with 

 the gut, other cavities or croca pullulate in the cell-blastema, and 

 the liver becomes conspicuous. ' Nowhere,' says Reichert, ' is the 

 new generation of cells within parent- cells so obvious as in the 

 blastema of the liver and pancreas.' l The primordial kidneys, or 

 de-azotising organs, have now begun to be developed between 

 the aorta and the intestinal plates, and the ducts of these, 

 together with the anal prolongation of the intestinal tube, open 

 upon the temporary tegumentary vent. In the Tadpole, as in a 

 Fish, the mouth is destitute of tongue, but at the entrance of the 

 mouth over the lips we find among the cartilaginous teeth at 

 that region numerous conical-shaped bodies. These labial papilla? 

 consist of an external border of prismatic epithelial cells provided 

 with cilia. The tongue makes its appearance when the fore limbs, 

 fig. 433, 54, 55, are evolved. The habits now alter: the Tadpole 

 no longer feeds on decomposing substances, and cannot live long 

 immersed in water. As the tail of the Tadpole atrophies, the 

 fungiform papilla? appear upon the nascent tongue, increase in 

 size, and accpiire the permanent complex form. 



Soon after the external gills have reached their full develope- 

 ment, they begin to shrink, and finally disappear ; but the 

 branchial circulation is maintained some time longer upon the 

 internal gills (p. 516, fig. 345); these consist of numerous short 

 tuft-like processes from the membrane covering the cartilaginous 

 branchial arches, fig. 433, 47 : they are protected by the growth 

 of a membranous gill-cover, which, as the external branchia? are 

 absorbed, leaves only one small external orifice, by which the 

 branchial streams admitted by the mouth continue to be expelled. 

 This orifice may be very plainly seen like a crescentic cicatrix, 

 a little behind and below the left eye, in the larva of the Rana 

 paradoxal 



The chief distinction between the fully developed branchial 

 circulation in the Batrachian larva and that of the Fish consists in 

 the presence of small anastomosing channels, between the branchial 

 artery and vein of each gill, proximad of the gill itself. 



The part which these anastomoses play will be understood by 

 the following description and figures of the vascular transformation 

 as observed in the Newt. When the gills are in full dcvelopcment 

 1 cccxxviii. 2 xx. vol. v. p, 77, preps, nos. 3286-3287, e. 



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