THE DEVELOPMENT OF ASTERINA GIBBOSA. 223 



They were then cut into series of sections in most cases 4^ ju 

 thick — in the case of the adults 7 jn; these sections were 

 mounted on hot water on the slide to flatten them, and stained 

 in either Grenacher's hsematcxylin or Mayer's carmalum. Two 

 points of interest in connection with this process may be 

 mentioned : first, I found that when the slide was transferred 

 from turpentine to absolute alcohol some of the sections were 

 sure to be lost, but that this could be avoided by placing the 

 slide for a minute or so, after taking it out of turpentine, into 

 oil of cloves, and thence into 90 per cent, alcohol; second, that 

 the readiness with which sections, especially when overcharged 

 with osmic acid, will take up either hsematoxylin or carmalum 

 is greatly increased by immersing them for twenty-four hours 

 in borax-carmine, though they do not acquire a particle of stain 

 from it. 



In the youngest stages the osmic acid produces too great 

 impenetrability for either celloidin or paraffin, and accordingly 

 my best results were obtained from some specimens preserved 

 for me by Sig. Lo Bianco in a mixture of three parts concen- 

 trated aqueous solution of corrosive sublimate, and one part 

 glacial acetic acid. This method also gives most excellent 

 preservation, though without that fine differentiation of the 

 tissues yielded by osmic acid and Miiller's fluid ; as during 

 the stages in question however the larvae consist almost exclu- 

 sively of epithelial cells, this is not a matter of any importance. 

 This second method was recommended to me by Dr. Eisig. 



The orientation of the specimens was one of the chief 

 difficulties to be overcome. I found that the best results were 

 given by horizontal sections perpendicular to the median 

 sagittal plane of the larva, and sections parallel to the disc and 

 perpendicular to the median axis of symmetry in the just 

 metamorphosed star-fish. The planes, to which in these two 

 cases the sections are cut parallel, viz. a median horizontal 

 plane in the larva and the plane of the disc in the adult, make 

 an angle of about 70° with each other ; and hence it is difficult 

 to correlate sections cut parallel to the one with those cut 

 parallel to the other. I shall call these planes the '' larval " 



