SPICULES OP SYNAPTA AND AURICULAlilA LARVA. 



485 



I may mention that after fixation it is well to slit open the wall 

 of the Syuapta so as to stain the integ'ument from the iuner side 

 as well as the outer. The integument is subsequently cut into 

 convenient pieces before mounting, and, like the Cucumai'ias 

 of Study IV, immersed for about five minutes in a saturated 

 solution of lichtgrun 1 in absolute alcohol, then washed well in 

 absolute, cleared in xylol, and mounted in balsam, the inner 

 side of the wall being placed uppermost on the slide. To 

 observe the spicules in side view, I cut transverse sections of 

 the undecalcified" body-wall about 12 ju to 20 fx in thickness 

 or slightly thicker. Numerous sections must be cut, since 



Text-i'ig. 1. 



Camera lucida drawing of a portion of a transverse section tlirough the 

 body-wall of tlie adult Sy napta in iiterens, sliowing the spicules in 

 position. The longitudinally-wrinkled condition of the dermal epi- 

 thelium and the dermal anchor-pockets are observable. These latter 

 are more apparent iu a surface-view of the integumeut. The 

 thickenings of the dermal epithelium are the sense-organs. (Reprinted 

 from ' Quart. Journ. Micro. Sci.,' vol. 49, p. 557.) 



the majority of spicules are fractured during the process of 

 cutting, and it is only occasionally that the knife happens to 

 fall just on each side of the (usually young) spicule instead of 

 on to it. 



My specimens of S. digitata were considerably older, 

 none being less than 5 cm. in length; nevertheless, I have 

 been able to observe all stages in development (though 



' In the plates a grey tint has been substituted for green. 

 ' Sections of the decalcifled body-wall I found to be useless. 



VOL. 51, PART 3. NflW SERIES. 36 



