2R 



long;) it already rorins a lai-f^j yv.it. ^^ . ■vi..ceral pimgs. 

 As tho ingestion of woody materials progresses, the caeciim 

 projocts more and more postoriorly, and in specimens 2 mm. 

 long (fir;*'''), it extends ntuch beyond the posterior adduc- 

 tor. Tho gills soon grow aroi.md the i'oot posteriorly and 

 in specimens 2 mm. long, ten to tv;elve days old, project 

 much beyond the visceral mass (fig. 7), This same stage 

 also shows the pericardial space, v;ith its contained and 

 associated structures, in the position v/hich it occupies 

 in the adult, distinctlj'' posterior to the large adductor. 

 And, in this, as in subsequent stages the visceral gan- 

 glion lies on the posterior end of the pericardial cavity. 



There ai-e a number of facts in the organization and 

 metamorphosis of the larva that seem to have a wider sig- 

 nificance. One of these is the sudden and complete loss 

 of the velum. Lovin thought that, in forms studied by 

 him,, it entered into the formation of the labial palps. 

 These structures are present in X. fimbriata only as the 

 small ridges on the sides of a sliglit groove around the 

 mouth; so that a form in which they may be said to bo ab- 

 sent, does not give necessary evidence against the deriva- 

 tion of tlie palps from the velum in forms in v/hich the 



