40 Charles Zeleny. 



In 1866 Agassiz described the development of branchiae and operculum in 

 Spirorbis spirillum, Gould (not Lamarck), and made out an alternate appearance of 

 the tentacles (branchiae). "The first tentacle appears on the right, next comes the 

 corresponding tentacle on the left and only later the rudiment of the odd opercular 

 tentacle (on the right side)." The rudiment of the operculum, though at first 

 somewhat resembling that of the tentacles, shows a difference from the start. 

 Claparede and Mecznikow ('69), on the contrary, make out a paired mode of forma- 

 tion of the branchiae in other species of Spirorbis. Willemoes-Suhm ('70) speaks 

 again of an alternate mode in Spirorbis. 



Giard ('76b) raised the larvae of Salmacina Dysteri. He found two lateral head 

 lobes each of which soon showed a threefold division. These divisions elongated 

 to form the first three pairs of branchiae. On each side there were two dorsal and 

 one ventral branchia,the latter, however, dividing into two on the fifth day, so that 

 there were then present eight branchial trunks, four on each side. The first pinnule 

 appeared on the eighth day on the upper third of the external dorsal branchia. 

 This is the only notice of pinnule formation I have found. 



In Manayunkia, a fresh water Serpulid, Leidy ('83), describes the head lobes 

 as showing the branchial digitations from the first trace of formation of the 

 former. 



Salensky (^^'^) likewise states for Pileolaria sp. that four branchiae and the 

 operculum appear at the same time from a median dorsal plate. The opercular 

 "anlage" is from the beginning three to four times as large as the branchial 

 "anlagen." In Salensky's words: "On voit d'apres cette description, que, chez 

 Pileolaria la formation des branchies et de I'opercule s'opere en meme temps, et 

 non comme Agassiz et Pagenstecher le montrent pour Spirorbis spirillum." 



Meyer ('88) describes the development of the branchiae in Eupomatus (= Hy- 

 droides). He makes out the appearance of the two head lobes from each of which 

 the three processes representing the first three branchiae sprout out. The develop- 

 ment was not carried further than this. This method of formation agrees also with 

 that described by Roule ('85) for the larvae of Dasychone. 



From the foregoing notes it is evident that further observa- 

 tions on the early development of the branchiae are necessary in 

 order to clear up our ideas regarding the matter, and when w^e 

 come to the opercular development we. have practically nothing 

 outside of the observations on the highly modified forms Spiror- 

 bis and Pileolaria except the short note of Fritz Miiller upon the 

 change of a branchia into an operculum. Regarding the forma- 

 tion of the rudimentary operculum there is nothing at all, and we 

 therefore get very little aid in our study of the correlation between 



