452 SOME ZOOLOGICAL METHODS. 



forceps behind the tentacles, so as to mechanically render 

 impossible their withdrawal, and immerses the anterior part 

 of the body in acetic acid, whilst at the same time an assistant 

 injects 90 per cent, alcohol through the anus. 



VOGT and YUNG (Anat. Comp. Prat., p. 641) say that Cucu- 

 maria Planci (C. doliolum, Marenzeller) is free from the vice 

 of expelling its intestines under irritation ; but they recom- 

 mend that it be killed with fresh water, or by slow intoxication 

 with alcohol, chromic acid, or sublimate added to the sea 

 water in which it is contained. 



Synapta may be allowed to die in a mixture of equal parts 

 of sea water and ether or chloroform (S. Lo BIANCO). 



846. Asteroidea. There are great difficulties in the way of 

 fixation here, too. It is quite possible to obtain a fixation of 

 the ambulacral feet, branchiae, and tentacles in the extended 

 state, by throwing the animals into boiling water, and then 

 bringing them into a fixing liquid. But this method has the 

 fault that the fixing liquid so employed only penetrates 

 extremely slowly into the interior of the animal, and therefore 

 does not give a good fixation of internal organs. 



HAMANN (Beitr. z. Hist. d. Echinodermen, ii, 1885, p. 2) finds 

 it preferable to inject the living animal with a fixing liquid. 

 The cannula should be introduced under the integument at 

 the extremity of a ray, and the liquid injected into the body- 

 cavity. The ambulacral feet and the branchiae are soon dis- 

 tended by the fluid, and as soon as it seems to have penetrated 

 sufficiently the animal is thrown into a quantity of the same 

 reagent. 



The study of the eyes presents points of special difficulty. 

 In order to study them in sections, with the pigment preserved 

 in situ, the eye should be removed by dissection, should be 

 hardened in a mixture of equal parts of 1 per cent, osmic acid 

 and 1 per cent, acetic acid, and imbedded in a glycerin gum 

 mass, or some other mass that does not necessitate treatment 

 with alcohol (which dissolves out the pigment, leaving the 

 pigmented cells perfectly hyaline). For maceration use one- 

 third alcohol, the aceto-osmic mixture failing to preserve the 

 rods of the pigmented cells. 



847. Ophiuridea. Should be killed in fresh water if it be 



