DEVELOPMENT OF THE BLOOD VESSELS IN THE FROG. 207 



the species investigated by Maurer, Bana esculenta, and in Bana 

 temporaria, which we have employed for our own observations. 



In support of this view, which, at first sight, may not commend 

 itself to morphologists, we would note the following points : — 



i. In the tadpoles of Bana temporaria which we have examined, we 

 have found a certain amount of variability in respect to the size and 

 relations of these branchial vessels, though an agreement in all essen- 

 tial respects. 



ii. In one specimen, but in one only out of a considerable number, 

 we have found a condition of things resembling that described by 

 Maurer. This tadpole measured 4 J mm. in length, but is thicker, 

 and slightly different in general shape to the ordinary tadpoles of the 

 same length. We have no special record with regard to its origin, 

 but can hardly doubt that, while slightly abnormal, it is really a 

 tadpole of Bana temporaria. 



In Fig. 5 a transverse section of this tadpole is given, passing on 

 the left side through the first branchial arch, and on the right side 

 through the first branchial pouch. The figure is diagrammatic, being 

 compounded from three or four successive sections, so as to show the 

 entire length of the branchial vessels. 



The efferent vessel is seen here to form a continuous trunk con- 

 necting together the truncus arteriosus and the aorta exactly as 

 described by Maurer. The middle portion of the vessel, opposite 

 the external gill, is wide and lacunar, while the dorsal and ventral 

 portions are cylindrical, with true epithelial walls. The afferent 

 vessel is present, but does not agree with Maurer's description, for 

 while it lies very close to the efferent vessel in the gill process, its 

 ventral end has no communication with the truncus, but lies some 

 distance from it. 



This is the only tadpole of this age in which we have found the 

 efferent vessel forming a direct connection between the heart and 

 the aorta. 



iii. We have already noticed that there are strong independent 

 reasons for thinking that the early development of the frog has been 

 considerably modified, and cannot be taken as affording a correct 

 view of its ancestral history. The branchial vessels afford an addi- 

 tional illustration, for it is clear that neither Maurer's account of 

 their development, nor our own, could possibly be interpreted as 



