SPOROCYSTS IN AN ANNELID. 



117 





On July 19, 1914, through the kindness of Dr. E. J. Lund, I 

 had the opportunity of examining another lot of these cercarise 

 from this same annelid. Some of these were observed to be 

 covered with an exceedingly thin hyaline membrane which be- 

 comes constricted at frequent intervals, the constrictions ulti- 

 mately being the only part of the 

 membrane that is visible. The cer- 

 carise from Hydroides, as was the case 

 with those from the scallop, exhibit 

 great activity, but the nature of their 

 movement is different. Instead of a 

 characteristic pecking motion of the 

 anterior end, the cercariae from the 

 annelid, occasionally, after lying mo- 

 tionless for a time, perform exceedingly 

 rapid wriggling movements. The an- 

 terior end of the body is provided 

 with a short, retractile boring appa- 

 ratus, shown protruded in Fig. 3. 



In addition to the various stages of 

 developing cercariae, other structures 

 were observed in these sporocysts. 

 With transmitted light these appeared 

 to be granular, but with reflected 

 light, or, with high magnification, they 

 appear to consist of minute oil drop- 

 lets, at least in part. In some cases 

 they were distributed rather uniformly 

 near the surface, in others they were 

 massed in the central region. 



The number of these sporocysts is 

 very great. In the first lot it was 

 estimated that there were between 900 

 and 1 ,000 sporocysts in the dish with 

 the annelid. After the worm had 

 been lying for a few minutes in a dish 

 of clean sea water to which it had been 



transferred, a number, 25 or more, of sporocysts made their 

 appearance on the bottom of the dish. The worm was then 



Fig. 3. Cercaria with fin-like 

 crest. The thin investing mem- 

 brane is indicated at the poste- 

 rior end. Length of body 0.17 

 millimeter, length of tail, 0.52. 



Fic. 4. Anterior end of a cer- 

 caria with a crest of slender, 

 cilia-like spines. 



