18 ANATOMY OF ASTRANGIA. 
PLATE VI. 
NEMATOCYSTS. 
The following quotations from Prof. J. Leidy, op. cit, may serve as an introduction to a study of 
the figures here given of the nematocysts found in Astrangia. He says: 
“ The filiferous capsules (nematocysts) of A. astreformis are of two principal varieties. The first 
variety consists of oval or ovoidal cells .05 mm. long by .0155 mm. broad, containing a spirally-wound 
thread. . . . The second variety consists of smaller cells, those of the tentacule measuring about 
.045 mm. by .0067 mm. and those of the white cords .03 mm. by .0112 mm.; and they contain besides 
a spirally-wound thread a style extending from one pole to about the centre of the cells. 
Both kinds of filiferous capsules, under certain circumstances not readily explained, eject their con- 
tained thread with an astonishing degree of rapidity, and in so doing the threads are absolutely turned 
inside out, as was first noticed by Agassiz and subsequently by Gosse, and remain attached to the 
emptied cells as long-extended tubes. From the smaller cells the style is also extruded and then 
appears as a more expanded portion of the thread, with which it is continuous at one end and with 
the capsule at the other. . . . An attentive examination of the extended thread exhibits a more 
complicated structure than would have been suspected, and, as remarked by Agassiz, who first 
detected the peculiar arrangement, its exact character is exceedingly difficult to ascertain and requires 
the utmost power of the microscope to analyze. In the case of the larger capsules a spiral arrange- 
ment is readily distinguishable, extending the entire length of the extruded thread. This arrange- 
ment, in some instances, appeared to me to depend on minute cilis, which project at right angles from 
the thread and apparently pursue a spiral course, as described by Agassiz and as represented 
but in other instances it appeared to me as if the thread during its eversion from the capsule assumed 
a spiral course within the portion preceding it, and that the thread externally at regular intervals 
with non-vibrating cilize 
“Tn the case of the smaller capsules the extruded style appears as a tube much dilated beyond 
its original calibre, narrowed at the extremities and longer than the cell which contained it, so that it 
appears to have been folded within itself. From the distal extremity of the stylous tube projects the 
everted thread, which at times appeared simple but at other times appeared to possess a spiral arrange- 
ment, like the coarser thread of the larger capsules. The tube derived from the style also presents a 
spiral arrangement apparently dependent upon long ciliz pursuing a spiral course, as represented in 
figure 16, or upon a twisting in the tube, as represented in figure 15.” 
The above description, the most complete which we have of the structure of the different kinds of 
thread-cells, or nematocysts, found in Astrangia, is from Dr. Leidy’s well-known paper on the marine 
invertebrate fauna of the coasts of Rhode Island and New Jersey.* This description was published in 
1855, before histological study had attained the development which it has in the present time.t 
* Contributions towards a Knowledge of the Marine Invertebrate Fauna of the Coasts of Rhode Island and 
New Jersey. By Joseph Leidy, M.D. Journ. Acad. Nat. Sci. Phil., Vol. III (second series). 
¢ As Mosely has well said in his report on the hydroid, aleyonarian, and madreporarian corals of the Chal- 
lenger expedition, ‘‘It would seem that a classification and nomenclature of the various forms of thread-cells is 
much needed, since these forms appear to be of classificatory value in the Coelenterata.” The Voyage of H. M.S. 
Challenger. Zoology. Report on certain Hydroid, Alcyonarian, and Madreporarian Corals procured during the 
voyage of H. M.S. Challenger in the years 1873-1876, p. 29, note. 
