520 METHODS FOR INVERTEBRATES. 



975. Larvae of Echinodermata (from instructions written down 

 for me by Dr. BARROIS). For the study of the metamorphoses of 

 the Echinoidea and Ophiuridea it is necessary to obtain preparations 

 that show the calcareous skeleton preserved intact (a point of con- 

 siderable importance, since this skeleton frequently affords land- 

 marks 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 larvse should be fixed in a cold saturated solution of 

 corrosive sublimate, for not more than two or three minutes, then 

 washed with water, and brought into dilute Mayer's cochineal 

 ( 235). 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. As above, but 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. 



Larvce 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 Pentacrinus larvse and of the young Synaptce formed 

 from Auricularia. Without this precaution you generally get 

 preparations of larvse either shut up (Pentacrinus), or entirely 

 deformed by contraction (young Synaptce). 



See also MACBRIDE on the development of Amphiura squamata, 

 Quart. Jo urn. Micr. Sci., xxxiv, 1892, p. 131 (osmic acid followed by 

 liquid of Muller and alcohol ; decalcification with nitric acid in alcohol ; 

 staining with Mayer's paracarmine or hsemalum) ; and SEELIGER on the 

 development of Antedon, Zool. Jahrb., Abth. Anat., vi, 1892, p. 161. 



MACBRIDE (Quart. Journ. Micr. Sci., xxxviii, 1896, p. 340) fixes larvse 

 of Asterina in osmic acid, brings into liquid of Muller for twelve to four- 

 teen hours, imbeds in celloidin followed by paraffin (see 171), and 

 stains sections with carmalum or Delafi eld's haematoxylin, best after a 

 foregoing stain of twenty -four hours in borax carmine. 



MAYER (Ghrundzuge, LEE and MAYER, 1910, p. 486) arranges a 

 number of fixed and stained Plutei on a sheet of gelatin foil gummed 



