ANATOMY OF ASTRANGIA. 19 
HISTOLOGY OF THE NEMATOCYST. 
Fig. 1.—Stroma from the epiblast, with large and small nematocysts in various conditions of 
growth. The nematocysts of the hydrocoralline, according to Moseley, “appear to be developed out 
of the nucleus of the ectodermic cells, the ectodermal cell becoming much enlarged and forming a 
wide chamber in which the process of development takes place. The ovoid nucleus becomes enlarged, 
together with the cell, but not at all in the same proportion, the cell always appearing as a wide 
cavity around it. The nucleus as it enlarges has a rounded nucleolus developed at one end of it. 
The nucleolus has large granules developed within it, whilst the nucleus becomes finely granular. 
In the next stage one large coil of the thread appears in the nucleus.” From the similarity of the 
fully grown and cell in Astrangia and some of the nematocysts of the hydrozoan hydrocoralline it is 
thought that a similar development occurs in Astrangia. 
a. Oval nematocyst. b. Club-shaped nematocyst. c,d. Nuclei. 
Fig. 2.—Club-shaped nematocyst. 
a. Cell wall. b. Style. c. Thread. 
Fig. 3.—Oval nematocyst. 
Figs. 4, 5—Club-shaped nematocyst. 
Fig. 6.—Inflated oval nematocyst with coiled thread. 
Fig. 7.—Two nematocysts with fully and partially protruded threads. 
Fig. 9.—Nematocyst with coiled thread retracted in cell. 
Fig. 10.—Distal end of the thread coiled into a conical spiral. 
Fig. 11.—Elongated oval nematocyst with thread coiled internally. a. Cell wall. 
Fig. 12—Nematocyst with partially extruded thread and with the retained portion irregularly 
coiled. 
a, Cell wall. b. Inflated region with “ stiff cilia,” or “spines.” 
Fig. 13.—Nematocyst with retracted thread. Lettering as above. 
Fig. 14.—Elongated oval nematocyst. 
Fig. 15.—Nematocyst with thread protruded but cut off just beyond the inflation which bears the 
“ stiff cilia.” 
Fig. 16.—The same as last figure. 
Figs. 17-21.—Different figures of the inflation of the thread, with spiral lines upon which the 
“ stiff cilia” are borne. 
Fig. 22.— 
Fig. 23.—Small elongated cell with protruded thread. 
Fig. 24.—Nematocyst with thread partially coiled in the cell and partially protruded. 
Fig. 25.—Pyriform shape assumed by a nematocyst. 
a. Cell wall. 
