736 UETICJTING ORGANS OF SEA NETTLES-MURBACH. 



These were: 



1. The nettling- organs are developed in cells derived from the 

 ectodeim.' 



2. The inner wall ot the nematooyst originates from the nucleus and 

 grows in the protoplasm around it.- In consequence of this growth, 

 a lighter area of secreted matter forms around the growing inner wall. 

 By the abstraction of water from the secreted matter it condenses and 

 shapes itself to the inner wall, and becomes the outer wall of the 

 nematocyst.^ 



3. The hollow thread grows in spirals around the nucleus, as a con- 

 tinuation of the inner wall of the nematocyst. The growing end is 

 nearest the nucleus. These growths are looked upon as the result of 

 the functional activity of the nucleus in the cell. 



4. When the development of the thread is complete, chemical changes 

 are assumed to take place in the cell, causing the outer wall of the 

 nematocyst to become firmer, and abstracting enough Avater from the 

 contents of the inner wall (exosmose), so that the diminished pressure 

 within will cause the thread to be drawn into the nematocyst. Tlie 

 spiral growth of the thread, during its development, favors a similar 

 arrangement in the nematocyst. 



5. When the thread is wholly within the capsule, the latter is rotated 

 in the cell, so that the opening in the outer wall is turned away from 

 the nucleus, and comes to lie directly under the opening in the cell. 

 body, for the discharge of the thread. 



0. The nettling organs are developed in more proximal parts of the 

 Cnidarian body (near the bases of the tentacles in Ilydromedusa', 

 but on the basal portion of the polyps in Siphonophora), and reach 

 their destination on the tentacles by active anueboid migration 

 {Hydra', etc.), or by displacement due to the rapid growth of the 

 tissues (Siphonophora). 



7. The stalks are probably outgrowths of the cell body, produced 

 after the migration of the organs. 



As these results were obtained from alcoholic material, save Hi/dra 

 which was used fresh, it was very desirable to verify them on fresh and 

 living marine animals, which I was enabled to do at Naples. 



In an appendix to the paper above mentioned, 1 gave, as a sort of 

 preliminary report, some of the principal results. 



The presence of nettling organs in the higher Protozoa, in the Cnida- 

 ria, in the Turbellaria, and in the Gasteropoda, makes it seem desirable 

 to compare the development, the structure, and the function of the-e 

 organs in the groups named. With this in view, representatives of two 

 of these divisions, not yet studied comparatively, have been collected. 



'The Microtomiat'a Vade-Mecum, A. B. Lee, 3d ed., 1893. 



-Eisig (Monogr. I. Capitellideu, p. 576), Perricr and f'lapande hold that tlie 

 nucleus is directly coDcerned iu the origin and forniatinn of the seta> of certaiu 



worms. 



■'I have siuce observed the stages of this inocess iu PhijsaUa. 



