108 



EENEST WAKKEN. 



the parasite actually invaded the tissues of the host or siniplj- 

 crept in the cavity between the perisarc and ccEnosarc. 



Text-fig. 2. 



Pinna (cat into tAvo) of S. l)idens infested with L. dispolians. 



In PI. I, figs. 1-6, are represented cross-sections at the six 

 levels indicated in Text-fig. 2. In fig. 1 the hydrorhiza of 

 the parasite {I\ i.) is seen on the side of the hydrocaulus of 



