42 



Charles Zeleny. 



to get at the method in which these primary processes branch later 

 on, I have designated them arbitrarily by the Roman numerals I, II 

 and III. I represents the most dorsal pair, II the middle pair and 

 III the ventral pair, R or L being prefixed to represent right or 

 left when there is any need for distinction between the two sides. 



Fig. 10. 

 Hydroides dianthus. Larvae. Stages of transformation from free-swimming to sedentary life. 

 Dorsal views. A — Free-swimming larva. Age, 9 days. Shows long apical cilium (X208). B — 

 Swimming but sluggish larva. Age, 9. days. Shows setae and shortened apical cilium (X185). 

 C — ^Attached larva (X90). Age, 17 days. Three pairs of head lobes. Beginning of secretion of 

 tube. D — ^Age, 17 days (X90). E — Age, 16 days (X85). F — Age, 17 days. Second of original 

 three pairs of branchiae shows secondary branches ( X 70). 



