PLATE XXVII. 
Figs. 1, la, lb, 1 c. — Sertularia exserta (p. 56). 
Fig. 1. — A colony ; natural size. 
Fig. la. — Portion of a colony ; magnified 25 diameters. The hydranths are here shown 
in their permanently exserted condition, and ectodermal bands are seen to 
extend from the body of the hvdranth to the walls of the hydrotheca. 
Fig. lb. — Base of a tentacle showing the cushion with its battery of thread-cells ; magni- 
fied 100 diameters. 
Fig. lc. — Thread-cells detached from the cushion ; magnified 150 diameters. 
Figs. 2, 2 a. — Sertularia abietina (p. 62). 
Fig. 2. — Portion of a colony ; natural size. 
Fig. 2a. — Portion of the same; magnified 15 diameters. 
