THE DEVELOPMENT OF ASTERINA GIBBOSA. 341 
They were then cut into series of sections in most cases 4} 
thick—in the case of the adults 7 w; these sections were 
mounted on hot water on the slide to flatten them, and stained 
in either Grenacher’s hematoxylin 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 hematoxylin 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 larve consist almost exclu- 
sively of epithelial cells, this is not a matter of any importance. 
This second method was recommended to me by Dr. Hisig. 
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” 
