260 



CEYLON PEARL OYSTER REPORT. 



durum. In this species they are extremely difficult to see, and are only about 

 5/i long and 2/x broad. 



Throughout the family the thread is apparently unbarbed ; nematocysts of Alcyo- 

 ninm with discharged threads are figured by HICKSON (1895). The nucleus of the 

 cnidoblast is usually long and curved (fig. 13), and stains very readily. Nematocysts, 

 similar to those occurring in batteries in the tentacles, are frequently to be found in 

 the ectoderm of the mouth disc, in the stomodseum, imbedded in the peripheral 

 portions of the mesenterial filaments, in the endoderm of the canals, and in some cases 

 in the mesoglo3a some little distance below the surface. They are extremely rare in 

 the ectoderm covering the general surface of the colony between the zooids. 



Genus. Species. 



Alcyonium digitatum . 



pachyclados . 



Lobophylum pauciflvrum . 



validum . 



crassum . . 



Sarcophytum roseuni . . 



latum . . 



glaucum . . 



ehrenbergi . 

 Sclerophytum tuberculosum 



densum . . 



capifak . . 



hirlum . 



gardineri . 



durum . . 



paliiuitum . 

 Hdero.eenia elizabetlue. 



Heliopom neniku . . . 



Claviikiria prolifera 



Size of nematocysts. 



7 |/i by 2/x to 3/x 

 8p to 9/j. by 2/i to 3/i 



6/t by 2/j 



6/1 to 7/i by 2/i to 2'5/i 



5-9/i to 6-9/i by 2/<. 



8-9/i to 9/i by 4/i 



6/t by 2/t to 3/i 



16jn to 22/i by 10/x to 14/i 



Thread 2/i broad. 



6/i by 2/i 

 7/i to 8/1 by 2/t 



7/i by 3ft 



8/1 to 9/i by 3/t to 3'5/i 



8/1 to 9/1 by 3/u, to 4/x 



12/i by 4-5/i 



5/i by 2/i 



6/1 by 2/i 



9/i by 2-5/x 



9/i by 2/i to 3/i 



8/1 by 2/i to 3/i 



10/i to 15/i by 2/i to 3/i 



Author. 



HICKSON 

 PRATT 



AsmvoiiTH 

 PRATT 



ASHWOUTH 



MOSKI.KY 



ASH WORTH 

 v. KOCH 



TENTACLES. 



When the tentacles of Alcyonium are expanded, their ectoderm is extremely thin, 

 and is composed almost entirely of batteries of cnidoblasts, columnar interstitial cells, 

 scleroblasts, and a few mucous cells. 1 have observed no granular gland cells such as 

 occur on the mouth disc. In the ectoderm of the body wall, nematocysts are 

 comparatively few in number, and are rarely seen in the ectoderm covering the 

 colony. 



Zoochlorella? are more or less fully described in a publication now in the Press 

 (PRATT, 1905). In a specimen of Sclerophytum densum some of the zoochlorelhv 

 are seen to have lost their cellulose cell walls (fig. 16). In such a case the 

 nucleus, chromatophore, and protoplasm of a cell exhibit unmistakable signs of 



