50 Charles Zeleny. 



Evidently the adult condition with an operculum situated on either 

 the right or the left side and having two rows of processes at its 

 distal end is not fully explained by the Cold Spring Harbor 

 observations. 



Only three larvae out of a great many sets of eggs started at Naples 

 lived through the period of attachment. Two of these were 

 H. uncinata and the other H. pectinata. These were first care- 

 fully observed only after they had developed up to the stage corre- 

 sponding to Fig. i6of H. dianthus. 



In Fig. 17B is represented a specimen of H. pectinata with essen- 

 tially the same characters as those of H. dianthus in Fig. 16. 

 The number of branchiae has, however, meantime increased and 

 there are here besides the opercula five branchiae on the left side 

 and four plus the bud of a fifth on the right side. The functional 

 operculum has the essential characters of the Serpula type (see 

 above). The new branchiae are being added on the ventral edge 

 of each of the branchial ridges. Both opercula have moved down 

 from the line of the branchiae and the gap left in the line by their 

 absence is being closed up. The character of the tube at this stage 

 is shown in Fig. 17c. The tube was so extremely irregular in 

 shape, largely because it was detached from the glass frequently 

 in order to facilitate observation. 



Practically the same conditions are shown at this time in H. 

 uncinata where there are on each side five branchiae plus the oper- 

 culum. The opercula here as before have the characters of the 

 Serpula type. (Fig. 170.) 



No further changes in the opercula were noticed for a long time. 

 Finally, six months after the fertilization of the ova, the animals 

 were again carefully observed, and it was noticed that the primary 

 functional operculum (left side) had fallen off (Fig. 17F) and in its 

 place a rudimentary one had developed, while the primary rudi- 

 mentary operculum of the other (right) side had developed into a 

 functional one. (Fig. i8a, b, c.) The two specimens of H. 

 uncinata retained their simple Serpula-like operculum longer than 

 did H. pectinata. 



Returning to the- specimen of H. pectinata as it was found after 

 the reversal of the opercula we find all the adult characters except 

 the full number of branchiae. The branchiae increase in number by 

 additions along the ventral edge of each branchial ridge. In speci- 

 mens at this stage there are beside the opercula seven branchiae 



