520 p. E. SMITH 



well formed lumina opening into a common cavity, this communi- 

 cating with the third ventricle by a wide ostium. 



In a larva of 13 mm. (figs. 5, 41) the wall of the velum, anterior 

 to the paraphysis, has become plicated, forming a plexus which 

 intrudes into the lateral ventricles (fig. 41). In addition to this, 

 there is an unpaired plexus which goes towards the floor of the 

 fore-brain, into the aula. These relations are the same as de- 

 scribed so clearly by Warren ('05) for Necturus. The paraphysis 

 is much convoluted and has a rich blood supply. The relative 

 distance from the tip of the velum to the epiphysis is much less 

 than in the previous stage. This is due apparently to the forward 

 growth of the mid-brain and the caudal growth of the telen- 

 cephalon. This shortening of the 'twixt-brain roof is also in- 

 creased by the straightening out of the brain which in Stage XII 

 has a strong diencephalic flexure. 



In a larva of 17 mm. the structures described in the previous 

 stages are present, as is true for the remaining stages. The 

 plexuses have become much more extensive, and the habenulae 

 are broadly connected across the mid-line so that the roof of the 

 third ventricle is quite thick for some distance in front of the 

 superior commissure. The epiphysis, because of its increase in 

 size, has come to overlap both the superior and posterior commis- 

 sures. As yet no secondary diverticula have appeared in it nor 

 could a communication between it and the third ventricle be 

 detected in this or the succeeding stages. Specimens of 19, 23, 26 

 and 30 mm., have been examined but need no description. 



In a 38 mm. specimen (fig. 40) the epiphysis has become divided 

 into secondary diverticula, the cells forming its roof having 

 become more flattened than those of the floor. In this, in a 52 

 mm., and in an 8 cm. specimen the blood supply of the epiphy- 

 sis and paraphysis is abundant, the supply of the latter being the 

 richest. In this organ a greater amount of space is taken up by 

 the blood vessels than by the gland itself. In an 8 cm. specimen 

 (full-grown adult) the epiphysis is relatively less extensive than 

 in the 38 mm. specimen. The superior commissure and haben- 

 ulae have undergone considerable growth. 



