1895. rilOCEEDINGS OF THE NATIONAL MUSEUM. 737 



Methods. — First of all, living Hydroid material was gathered so as 

 to examiue the organs in their natural condition, and also to test mj- 

 conclusions in regard to migration and development. As my previous 

 observations had not taken into account the Actinia', tlioy were first 

 examined. Fresli cerata of living ul^oJidiw were given some attention, 

 and many specimens were preserved for later histological work. 



The methods employed were largely those already in vogue and 

 described, only moditied enough to suit the circumstances.^ 



For the examination of living tissue, a bit was placed in sea Avater 

 on a slide, and a very dilute solution of aqueous methylin blue was 

 added. The mass was then either only slightly compressed under the 

 cover glass, or it was first teased, and then the elements were further 

 isolated under the cover glass by lightly ta])ping on tlie latter with a 

 pencil or other suitable object, until the desired result was obtained. 



For preservation, Hydroids were killed by quickly pouring over 

 them, placed in as little sea water as would keep them expanded, an 

 acidified solution of corrosive sublimate, in 30 or 50 per cent alcohol. 

 After some minutes they were removed from this mixture to the diluted 

 pure solution, left for one-quarter hour,'^ then transferred to 70 per cent 

 alcohol for one hour, and finally put up in 80 per cent alcohol. 



Small Actini{T3 were similarly treated except that the solution for 

 killing was first heated. (!)n some of the larger Actinia* the narcotiza- 

 tion process was used previous to fixing, but with indifferent success. 



The few Siphouophora preserved were treated essentially like the 

 Hydroids, except that they were killed by pouring into the least possible 

 quantity of sea water that would keep them expanded an acidified 10 

 per cent solution of copper sulphate, to which was added a little cor- 

 rosive sublimate solution. 



On some Turbellaria and on u^^oUdia;, Kleinenberg's fluid worked well 

 for killing and fixing. After thoroughly washing in 70 per cent alcohol 

 they were placed into 80 per cent. Other ^Uolidicv were treated quite 

 like the Hydroids. On still others, dilute Flemming's fluid was used as 

 a fixative, and with good success. For preserving the external form, 

 killing with glacial acetic acid, added in abundance, and immediately 

 removing to weak alcohol, proved most effective. Yet much depends 

 on the proper manipulation of the animal while the tissues are fixing.^ 



The material to be sectioned was stained with Mayer's hannalum, 

 picro-carmine, or with borax-carmine. 



Historical. — The question of the transposition of nettling organs, for 

 they are rarely ever used at the point where they develop, has long 

 been an interesting one. For the Siphouophora, bearing capturing 

 filaments, it was long ago settled by Professor Leuckart,^ that the 



'The Microtomist's Vade Mecum, A. B. Lee, Sd ed., 1893. 



'This time varied, of course, depending on the size and nature of the object. 



3 One such well-preserved specimen is due to the skilll'ul hand of Signor Lo I3ianco. 



* Zoologische Untersuchungen ; I, Die Siphouophoren, 1853. 



Proc. N. M. 93 47 



