242 



ZOOLOGY. 



which tends more and more completely to separate off 

 the pericardium from the rest of the crelom ; but to the end 

 of tadpole life a pair of pericardia-peritoneal pores are left, 

 connecting the two regions of the cceloin. At this stage, 

 therefore, the pericardium has considerable resemblance to 

 that of the dogfish. The adult condition is produced by the 

 shifting back of the heart as the lungs develop (compare 

 fig. 91). 



16. Further Development in the Tadpole. Meanwhile 

 numerous other changes have been taking place. The whole 



Fig. 124. CIRCULATION IN THE TADPOLE. 

 11 Vitelline Vein" is the same as " Sub-intestinal Vein." 



body has grown in size, and the tail has elongated greatly 

 and become an active swimming organ, in which fish-like 

 myomeres are very obvious. There is a continuous median 

 fin to the tail, along both dorsal and ventral edges, and it is 

 interesting to note that this extends a little in front of the 

 cloacal aperture, which consequently is shifted a little to 

 one side, as in Amphioxus. The shifting is, however, to the 

 right, not the left. 



The intestinal region of the alimentary canal has grown 

 much faster than the body, and forms a long coil in the 

 ccelom. It remains of uniform diameter. All the yolk is 



