48 



Charles Zeleny. 



upon specimens before a count was undertaken. In this count 

 twenty individuals were noted. All without exception, the former 

 as well as the latter, showed the functional operculum appearing on 

 the left side. 



Fig. 17A shows the rudimentary operculum at a slightly later 

 stage in which it has more definitely assumed its typical condition. 



Fig. 16. 

 Hydroides dianthus. Age, 34 days. Dorsal view (X38). On left side is functional operculum 

 of Serpula type with naked stalk and cup with one row of serrations. On right side is rudimentary bud 

 developed from the base of the cast-off second branchia of that side. The three pairs of typical branchiae 

 also are shown. 



The condition at this time resembles very closely that of the adult 

 Serpula, as the functional operculum as shown in Fig. l6 is without 

 doubt of the Serpula type. The further changes were not followed 

 in H. dianthus, the species at Cold Spring Harbor, but were made 

 out in the two Naples species, H. pectinata' and H. uncinata. 



