SOME METHODS FOR LOWER ANIMALS. 483 



of the different organs, and show the calcareous skeleton 

 preserved intact (a point of considerable importance, since 

 this skeleton frequently affords landmarks of the greatest 

 value), and that give clear views of the region of formation 

 of the young Echinoderm (which is generally opaque in the 

 living larva). They should also possess sufficient stiffness to 

 allow of the larva being turned about in any desired way, 

 and placed in any position under the microscope. 



Pluteus larvae should be fixed in a cold saturated solution 

 of corrosive sublimate, in which they remain not more than 

 two or three minutes. They are then washed with water, 

 and brought into dilute Mayer's cochineal ( 230). This 

 should be so dilute as to possess a barely perceptible tinge 

 of colour. They should remain in it for from twelve to 

 twenty-four hours, being carefully watched the while, and 

 removed from it at the right moment and mounted in balsam, 

 or, which is frequently better, in oil of cloves or cedar- wood. 



Auricularia and Bipinnaria. The method described above 

 is equally applicable to these forms, and seems to be alto- 

 gether the best method for the study of the metamorphosis 

 of Bipinnaria. The earlier stages of the metamorphosis of 

 Auricularia are better studied by fixing with osmic acid, 

 staining with Beale's carmine, and mounting in glycerin. 



Larvss of Comatula are best fixed with liquid of Lang, 

 and stained with dilute borax-carmine. It is important (for 

 preparations that are not destined to be sectioned) to use 

 only dilute borax-carmine, as the strong solution produces 

 an over-stain that cannot easily be reduced. 



Narcotisation by chloral hydrate before fixing is useful, 

 especially for the study of Pentacrinns larvae and of the 

 young Synaptse formed from Auricularia. Without this 

 precaution you generally get preparations of larvae either 

 vshut up (Pentacrinus) , or entirely deformed by contraction 

 (young Synaptae). 



See also MACBBIDE on the development of Amphiura squamata, Quart. 

 Journ. Mic. Sci., xxxiv, 1892, p. 131 ; Journ. Roy. Mic. Soc., 1893, p. 117 

 (osmic acid followed by liquid of Miiller and alcohol; decalcification with 

 nitric acid in alcohol ; staining with Mayer's paracarmine or hiemalum) ; 

 and SEELIGEE on the development of Antedon, Zool.Jahrb., Abth. f. Anat,, 

 vi, 1892, p. 161 ; Zeit. f. wise. Mik., x, 2, 1893, p. 229. 



MACBRIDE (Quart. Journ. Mic. Sci., xxxviii, 1896, p. 340) fixes larvre of 



