11 



rondition the tontaclos and Ixxly Avail of the aiithorodijp 

 are very transparent, and many features of the anatomy 

 can be seen wilhout dissection.* 



The details of anatomy that can lie seen in a livino- 

 anthocodia are as follows: — From the mouth theie hangs 

 down into the body cavity a short opafjiie throat — the 

 stomodieum (AV.)- -which opens freely below. At this — 

 the lower — aperture six short sinuons cords, the mesen- 

 terial filaments, arise attached to the free edges of six 

 very thin vertical jdates — the mesenteries (conf. PI. I., 

 fig. 4, PI. II., fig-. 15, M>it.) — and, in addition, there are two 

 C(nds which pass straight down into the cavity of the 

 polyp attached to the free edges of the two remaining 

 mesenteries. These two straight cords are called the 

 dorsal mesenterial filaments, and tlie mesenteries which 

 support them the dorsal mesenteries. The other mesen- 

 teries are called the dorso-laterals, ventro-laterals and 

 ventral s respectively. 



Further details can only be studied in preparations 

 made for microscopic examination. 



Nematocysts. — The pinnules of the tentacles bear a 

 numbei' of very minute stinging organs — the nematocysts. 

 They are extremely small (0"00T5mm. in length), and may 

 be easily overlooked. They aie oval in shape, and when 

 irritated discharge a plain unainied thread (PI. II., hgs. 

 S, 9, 10 and 11). Fa(di nematocyst is formed within a 

 specialised ectodermal cell called the " cnidoblast." 



The ST()M()]):ErM is lined internally by a columnar 

 ciliated ejiithelium, usually thrown into a number of folds 

 in the preparation. On one side there is a groove lined 

 by specialised epithelium armed with relatively long 

 * The transparency varies iu specimens from different localities. In 

 some cases there are so many spicules in the anthocodia that the trans- 

 parency is very considerably diminished, Tlie figui'c 4 in Plate_l. was 

 drawn from a Plymonth specimen. 



