454 Simon Henry Gage 



surface and the development of the sensory papillae in the 

 characteristic curved line interrupted by the eye (PI. VIII, 

 fi?- 50)- Looked at in a strong light the eyes appear in a 

 dorsal view like clear spaces ; looked at from the side the 

 black pigment, especially in the dorsal half, is very evident. 

 The mouth in this stage is precisely the same as the larva to 

 all appearance and so is the general coloration of the body. 

 In a somewhat later stage the eyes are still more evident, but 

 appear dull and as if covered by only a semitranslucent mem- 

 brane. The mouth has no longer the wide open appearance 

 of the larva but has become greatly contracted ; the dorsal and 

 ventral lips are becoming fused and the oral tentacles arrange 

 themselves as shown in figure 23. The appearance is exactly 

 as if the papillae or tentacles were to form the basis or found- 

 ation for the future teeth. Several days (20) later the eyes are 

 less turbid and the oral tentacles have lost their branched ends 

 and have become blunt papillae. In one kept in a large glass 

 vessel with sand and stones, changing the water frequently, the 

 changes just described were gone through in 25 days. But 

 it is believed that nearly as many more days are needed to de- 

 velop the large, clear eyes of the adult form and the enlarged 

 sucking discwnth horny teeth ; so that with those investigated 

 by me the metamorphosis cannot be said to go on ver)^ rapidly, 

 but rather, ver>' slowly. One of the striking external changes 

 also is the gradual darkening from a brownish gray to a blue 

 black, which is so rich and soft that it appears like velvet. 

 The pineal eye then appears like a snow white, rounded spot. 

 Later it is partly overshadowed by the thickening epithelium 

 and looks dull (PI. VIII, fig. 50). A striking change in atti- 

 tude also occurs. The animal rests dorsal side up and not on 

 the left or the right side as with the larva. 



Corresponding with the external changes, there are profound 

 internal changes. The intestine no longer opens into the 

 bronchus, but a new oesophagus is developed along the dorsal 

 wall of the bronchus and finally opens cephalad of it very 

 near the mouth. The gills cease to be in a common chamber 

 and are divided, each one forming a pouch which opens to 

 .the exterior by the branchiopore as in the larva and into the 



