456 SOME ZOOLOGICAL METHODS. 



fine dissociations of the connective, sensory, and urticant cells 

 of the ectoderm, and after removal of the epidermis allow of 

 the demonstration of ganglion-cells and the supporting 

 lamella. Picro-carmine may be used for staining. 



850. Hydroidea, Polypoid Forms. For suitable narcotisation 

 methods see those quoted in last section. 



Fixation. In general the polyps may be very well killed in 

 saturated sublimate solution, in which they should be plunged 

 for an instant merely, and be brought into alcohol. The 

 solution should be employed cold in general for G-ymnoblastea, 

 hot for most Calyptoblastea. 



Ether attentively administered gives good results with Cam- 

 panularidae. Hydra is very easily killed by treatment with a 

 drop of osmic acid on a slide. BKECKENFELD (Amer. Hon. Mic. 

 Journ.j 1884, p. 49) obtains good results by heating the ani- 

 mals in a drop of water on a slide for from three to five seconds 

 over a petroleum lamp. The methods for sections are the 

 usual ones. 



The methylen-blue method of intra vitam staining is appli- 

 cable to this group, see, inter alias, ZOJA, 1. c., 114. 



851. Medusae: Fixation:. There is some difficulty in properly 

 fixing the forms with contractile tentacles, which easily roll 

 up on contact with reagents. The best results I have had with 

 these forms have been obtained by means of VAN BENEDEN'S 

 acetic acid method, 53, followed by alcohol. A similar 

 method, with the difference that a mixture of chromic acid 

 and alcohol is used for washing out instead of pure alcohol, is 

 recommended by DE CASTELLAKNAU (La Est. Zool. de Napoles, p. 

 133) for Oceania, .Lizzia, Bougainvillia, Podocoryne, Syncoryne, 

 &c. The secret of success with the long-tentacled forms lies 

 in a trick of manipulation. Put sufficient acetic acid into a 

 deepish dish, hold it in your left hand (or, better, in both 

 hands if you have an assistant), and keep it moving in a 

 circle so 'as to communicate a vortex motion to the liquid. 

 Take up a medusa in a spoon with as little sea- water as 

 possible, and throw it into the moving liquid, and keep the 

 liquid steadily swirling round so as to cause the tentacles to 

 trail out at full length behind the animal until it is thoroughly 

 fixed, then pass carefully into alcohol. Do not, unless you 

 are very expert, try to fix more than one medusa at a time ; 



