734 URTICATING ORGANS OF SEA NETTLES— MURBACH. 



Their position on the surface of the tentacles is generally marked by 

 a hair-like ]n'ojection— ^Ae cnidocil~^^hGVQ, nettling organs stand 

 singly. In some cases the organs are collected at the tips of the tenta- 

 <,-]es in the form of nettling l-nohs, aud in others they are grouped on 

 smaller branches of the capturing filaments in the form of nettling 

 batteries. In the latter case cnidocils are seldom present. 



The nettling organs consist essentially of a nucleated, more or less 

 modified, cell, the cnidohlast, which contains a capsule, the nematocyst, 

 inclosiug a much coiled hollow thread— ///t' nettling thread. 



The cellhody is somewhat cup or goblet shaped, having, however, 

 only a small aperture at the top, for the discharge of the little weapon. 

 At the side of this opening the cnidocil stands, and at the opposite end, 

 the cell-body is drawn out in the form of a foot or stalJc. In the lower 

 €nidaria this stalk is simple, but in some of the more specialized 

 forms of the Siphonophora the stalk and the lower portions of the 

 cell-body contain S2)iral contractile fibers.^ 



The nucleus of the cell is almost always in a mass of granular proto- 

 l)lasm— the base of the goblet-shai)ed part-^iust at the side or under 

 the capsule, which is contained in the hollow of the goblet. 



The nematocysts nuxy be si)herical, oval, or cylindrical. Each is a 

 ■iloubleiralled capsule, transparent enough to enable one to see the tiuid 

 contents and the tortuous thread within. The outer wall is very thick 

 and similar to chitin. The opening in its end comes just under the 

 opening of the cell-body. The very thin inner wall is closely applied 

 to the outer wall, and, passing through the opening in this, becomes 

 insensibly continuous with the nettling thread. 



The hollow nettling thread, in its resting condition, is turned, outside 

 in, back into the nematocyst, lying coiled up more or less regularly in 

 the fluid contents of the latter. In this condition its present lumen 

 (tlie walls of which constitute its outer surface after discharge) is filled 

 with a viscid fluid, which gives the discharged thread its adhesive and 

 irritating character. The discharged thread is often twenty times 

 loDger than the longest diameter of the capsule. The thread of the 

 spherical capsules is usually a simple slightly tapering tube, having on 

 its outer surface three spiral rows of very fine barbs. In the case of 

 the oval capsules, a widened cone shaped basal portion is joined to 

 the thread. A small intermediate piece bears some very small, back- 

 wardly directed spines, while on the basal portion near its junction 

 with the intermediate piece there are three large spines directed back- 

 ward. The thread of the cylindrical capsules differs, principally from 



' Heretofore the appearance caused by the spirals was mistaken for cross striatious, 

 iiucl the parts iu question were thought to represent cross striped muscle. But after 

 finding the spiral filaments, I still wish to assert a muscular nature for them, as 

 stated iu a previous paper. Recently Schneider (Zool. Anz., No. 464) conlirmed the 

 presence of spiral structures iu VeleUa, hut he denies their contractile nature, 

 without giving substantial reasons. Since spiral muscles are now found in Cepha- 

 lopods, I hold to my interpretation. 



