740 URTICATING OliGAXS OF SEA NETTLES— MUEBACH. vol.xviii. 



As already stated, I demoustrated tLat the nematocyst is of hetero- 

 geneous ori(/in ; the inner wall being derived from the nucleus, "^hile 

 the outer one results from the secretions arising around the former 

 during its growth. Also that the thread develops around the nucleus 

 of the cell, and not around the wall of the nematocyst, as has been 

 lieretofore held. 



These points were now reexamined in living and fresh material, espe- 

 cially in vSiphonophora and in Medusiie. The Actinia^ were also prelim- 

 inarily examined. The same course of development as has been 

 described from alcoholic specimens could now be most beautifully 

 observed, the thread being slightly stained by methylin blue. With 

 the nucleus somewhat stained the observation Mas very easy and 

 decisive. 



In the Actinije observation becomes much more difficult, because of 

 the small size of the nettling organs of most of them. Anemo)w sulcata, 

 tlien at hand and a sufficiently typical specimen, was first examined. 

 The early stages of both capsule and thread resemble very closely 

 those of the cylindrical ones of the Siphonophora. The inner wall of 

 the nematocyst early takes on a curved form, the nucleus with encir- 

 cling thread lying in the concavity. The spirals of the thread do not 

 seem to be so regular as those of the Hydrozoa examined. But they 

 could be seen in greater number. By inducing a current under the 

 cover glass the observation may be made more certain, because different 

 views of the uematoblast are thus obtained. Both Adavisia rondelctii 

 and Astroides cali/culans were sufficiently examined to confirm what I 

 had observed in the other form. The latter is not a suitable form for 

 this work, on account of the minuteness of its nettling organs. 



It is my intention to subject this matter to a more thorough examina- 

 tion in Actinia^; but even now I believe we are warranted in conclud- 

 ing that the development of the nettling organs is the same for all the 

 Cnidaria. 



The Turbellaria collected have not yet been examined for the devel- 

 opment of their nettling organs, in the light of these newer observa- 

 tions; f hough in one form previously obtained at Leipzic, some 

 apparently undeveloped nematocysts were found, that lead me to look 

 for a similar plan of development to that already established for the 

 Cnidaria. 



The ^olidia obtained at Naples are under investigation, but so far 

 no results are definite enough to be stated. 



In conclusion I wish to thank the Director, Dr. Dorn, for courtesies 

 while at the Naples Zoological Station, also the Secretary of the Smith- 

 sonian Institution, and the committee in charge, for the privilege of 

 occupying the table. 



