I'l.ATH XVII. 



Fig. 1 and - are front and lateral views, respectively, of two specimens of 

 Tonmria rHlcri. These are not drawn to exact measurements, 

 so the difference in size does not necessarily mean that the 

 specimens were thus different. Both were practically at the 

 climax of larval life. 



Figs. '.', and 4 are both from the same individual of /'. httblxmli. 4 shows tie- 

 larva as it appeared when first brought to the laboratory, while 

 ■i represents the condition it was in after a day's sojourn in the 

 aquarium. 



Pig. 5. -Represents, in optical section, the esophagus, is., and a small 

 portion of the stomach, st., of the fully developed larval stage 

 of T. hubbardi. duly six gill pockets are shown in this case, but 

 at a slightly later time another, making seven, was present. The 

 notoehord is seen at n.c. All remaining figures <in: from T. 

 ritteri. 



Fig. ti. — Is from a section of the ectoderm partly, re. or., oral, and partly 

 (the remainder) extra oral, immediately after the beginning of 

 metamorphosis. It should be compared with Figs. 7 and S. 



Fig. 7. — From a section, similar in position to that shown in (3. of the ecto- 

 derm of a larva well advanced in metamorphosis. 



