] 12 ERNEST WAKREN. 



Fig. 6. — x 325. Cross-section along the line 6, 6 of text-fig. It 

 shows the junction of the hydranth and hydrorhiza-sac of the parasite. 

 e. H. is the remnant of the ectoderm of the host on the perisarc-wall. 



Fig. 7. — X 700. Cross-section through the coenosarc of the host in 

 which is embedded the hydrorhiza of the parasite surrounded )jy 

 perisarc secreted by the Sertularia. Nematocysts (n) occm- in the 

 ectoderm. The endoderm-tube of the host is composed on one side of 

 especially elongated cells {gl. c.) which are filled with refringent yolk-like 

 globules. Similar globules occur in certain swollen cells {yl. c.) in the 

 ectoderm on each side of tlie endoderm-tulie. 



Fig. 8. — x 600. Oblique cross-section through hypostome, and 

 longitudinal section through tentacle of parasite. It shows the modified 

 endodeim of the hypostome, consisting of elongated nan-ow cells with 

 deeply staining granules. A piece of the hydrotheca of the parasite is 

 seen at p. P. 



Explanatory References for Plate and Text-figures. 



a, h. Hydrothecaj and hydrauths of parasite. A., B., C. D. Hydro- 

 thecse of host infested with parasite, b. H. Base of hydranth of para- 

 site, e. h. Endoderm of hypostome. e. H. Ectoderm-remnant of host. 

 g. A. Growing apex of parasite, y/. c. Swollen cells df ectoderm 

 filled with globules, gl. e. Endoderm cells filled with globules, h. s. 

 Hydi'orhiza-sac of parasite. ^. p. Inner layer of perisarc. I. e. Lining 

 ectoderm of perisarc-wall of host. n. Nematocyst. 2^- ^- Perisarc 

 secreted l^y host and shutting off the parasite, p. P. Perisarc of para- 

 site. P. i. Parasite inside host. P. o. Parasite outside host. 1, 1 ; 2, 2 ; 

 3, 3 ; 4, 4 ; 5, 5 ; 6, 6. Planes in Text-fig. 2 through which the sec- 

 tions drawn in the Plate were taken. 



