95 



NOTE ON LARVAE OF OPTIRYOTROCIIA 

 PUERILIS. 



BY A. D. PEACOCK, M.Sc. 



On March 5th, 1920, Mr. Storrow drew my attention to the 

 large numbers of Ophryotrocha puerilis in one of the tanks. On 

 examination many of these were found to be egg -bearing, and at 

 various times during the next fortnight batches of eggs were 

 obtained from them. The eggs, however, never developed beyond 

 a condition in which sixteen cells could be counted. During the 

 next month microscopic examinations of watch glass skimmings 

 of the surface of the tank and also of one coimected with it revealed 

 swarms of larvae with only one segment posterior to that of the 

 head. Larvae with four to six hinder segments were also found, 

 but only in very small numbers. Figures of larvae are given, 

 drawn from the living specimens, since those of Braem* and 

 Korschelt|, whilst drawn from material about the same age as 

 mine, do not indicate certain features. For instance, Braem's 

 figure of the larva with one posterior segment is not at all a 

 characteristic likeness. 



The larva moves forward and rotates on its long axis. The 

 eyes, by reflected sunlight, are red. The cilia of the anterior and 

 posterior bands are strong, coarse and long, but those of the middle 

 band and those in the regions of the mouth, anus and posterior 

 segment are much finer. Opportunity has not permitted me to 

 distinguish the precise disposition of the cilia in the mouth region, 

 but the drawings illustrate what I have observed. In the stomo 

 daeal region an undulatory movement is visible, and has been 

 indicated b}^ a line in the drawing. A clear zone is very apparent 

 between the head and posterior segments. A pair of little knobs, 

 placed close together like terminal cirri, have been observed on 

 the posterior segment of two specimens. 



Figure 3 of a larva with three posterior segments is very 

 similar to one of Korschelt's, except that his does not indicate 



* 1893. Braem, F. Zur Ent. von Ophnjofrorhi puerilis. Zcitschr. w. Zool., Ivii., pi XT. 

 t 1893. Korsdielt, E. IHcl, PI. XIII. 



