l88S,J NEW-YORK MICROSCOPICAL SOCIETY. 135 



Now, as to the mode of emission of the thread (or ecthoi-ceum, 

 as it is technically called), Mr. Gosse says, with reference to a 

 Madrepore generically related to the one we are examinin^^ : 

 " On several occasions of observation on the chambered cnidce 

 of Cyathina Smithii, I have actually seen the unevolved portion 

 of the ecthoraum running out through the center of the evolved 

 ventricose portion;" and in another place he speaks more par- 

 ticularly thus : " I have offered a conjecture that the projection 

 of the thread is an evolution of its interior, and I believe that 

 it is a complete one through its whole length. I have, even since 

 I wrote that conjecture, seen an example of the process, which 

 I can scarcely describe intelligibly by words, but the witnessing 

 of which left on my own mind scarcely a doubt of the fact. It 

 was effected not with the flash-like rapidity common to the pro- 

 pulsion, but sufficiently slowly to be watched, and by fits or Jerks, 

 as if hindered by the tip of the lengthening thread being in con- 

 tact with the glass. In consequence, probably, of this impedi- 

 ment, it took a serpentine, not a straight form, and eac/i bend of 

 the course was tnade and stereotyped (so to speak) in succession, 

 while the tip went on lengthening ; and the appearance of this 

 lengthening tip was exactly like that of a glove finger turning 

 itself inside out." In the "Standard Natural History" it is 

 said, with reference to the common Hydra, " Now when any 

 stimulus brings a cnidocell into activity, it forcibly ejects the 

 larger part of the tube by a process of evagination or a turning 

 of this part of the tube inside out, as one turns the finger of a 

 glove: this movement is quickly followed by the ejection of the 

 smaller part of the tube in the same manner, by evagination." 

 In Huxley's "Anatomy of Invertebrated Animals," referring to 

 the nematocysts of the coelenterata generally, it is stated that 

 " the filament is hollow, and is continuous with the wall of the 

 sac at its thicker or basal end, while its other pointed end is 

 free. Very slight pressure causes the thread to be swiftly pro- 

 truded, apparently by a process of evagination, and the nema- 

 tocyst now appears as an empty sac, to one end of which a 

 long filament, often provided with two or three spines near its 

 base, is attached." 



In these last quotations the use of the word evagination is 

 noticeable, because in the one it is employed with a definition 

 which makes very clear what the writer meant, while in the 



