A COLLECTION OF HYDRO! I»S. 853 



ectodermal sheet (e.(/.), it has a definite opercuhuu (uj).), and the modi- 

 fied hydraiith has a clump of tentacles (te.). 



Fig. 21. — X -iS. Small piece of colony of Sertularella cam panu- 

 lata sp. II. creeping on weed. 



Fig. 22.— X 220. Median longitudinal section through the liydr.inlli, 

 hydrocaulus. and hydrorliiza of S. campanulata. The opening in tlie 

 diaphragm is excentric, the perisarc of the hydrotheca is much thinner 

 on the side facing the hydrorliiza than on the opposite side, and the 

 hydrocaulus is set at an angle of aljout i-5^ to the liydrorhiza. 



Fig. 23. — X 1 80. Front view of hydrotheca of S e r t u 1 a r i a a c a n t h o - 

 stoma Bale, showing four outer teeth and four inner teetli on eacli 

 side. 



Fig. 2-i. — -X 180. Side view of hydrotheca of S. acanthostoma, 

 showing the lower peg of chitin {L}^). 



Fig. 25. — X 300. Median longitudinal section of hydrotheca and 

 hydranth of S. acanthostoma, showing sheet of ectoderm lining 

 hydrotheca, with median thickening and battery of elongated nemato- 

 cysts (B.ii.) lying on special platform (iM.) of perisarc. 



Fig. 26. — x 850. Median longitudinal section through edge of 

 hydrotheca and ectoderm sheet of S . acanthostoma. The thickening 

 of the sheet with the battery of elongated nematocysts (B.n.) and tlie 

 outer clothing of coralline sea-weed {C.W.) are well seen. 



Fig. 27. — X 200. Side view of piece of stem of Paragattya inter- 

 media sp. 11. The hydrothecse usually possess one pair of large lateral 

 teeth (2, 2), but occasionally there may be two pairs (2, 2 ; 2a, 2a). The 

 nematophores should be specially noticed ; the jointed lateral nemato- 

 phores (/.), the median nenuitophore aliove the hydrotheca (sup.n.). and 

 the mesial nematophore {iii.n.). not adherent to the hydrotheca, which 

 lies below. 



Fig. 28. — x 80. Side view of small piece of pinna of Aglaophenia 

 parasitica sp. n. 



Fig. 29. — x 200. Front view of hydrotheca of A. parasitica, 

 showing the arrangement of teeth. 



Fig. 30. — X 30. Side view of male corbula of A. parasitica, 

 showing the lateral prolongations (/./.) of the leaflets. 



Fig. 31. — x 30. Side view of female corlnila. 



Fig. 32. — x 35<,t. Transverse section through the hydrorliiza of A . 

 parasitica, showingthe sucker penetrating into the coralline sea-weed. 

 The sucker generally passes through the cortex down to the medulla of 

 the plant. The sucker is formed of modified ectoderm. In the neigh- 

 bouring ectoderm there are rounded cells (i/.e.) filled with glolmles of 

 homogeneous substance. 



