180 HIROSHI OHSHIMA 
To kill and fix the larvae I used a chromo-acetic mixture 
containing a shght amount of osmic acid. Later examination 
showed that this fixative proved very satisfactory for the study 
of tissues, but for embryological purposes it is bad, since the 
free cells contaimed in the hydrocoele and enterocoele are fixed 
in a very expanded state, almost fillmg up the lumen of these 
vesicles. Newth used Bouin’s picro-formol-acetic and 
Flemming’s strong solution, and seems to have experienced 
a similar difficulty, judging from his following remarks: ‘ Even 
after the tentacles are well established, and can be protruded 
and retracted, their lumen is obliterated in some places by 
the vacuolated inner ends of their cells ’, and ‘ there is a complete 
suppression of the typical curved hydrocoele crescent owing to 
the large size and close crowding together of its lobes and to the 
thickness of their walls’ (86, p. 636). 
The late Professor Mitsukuri seems to have used acetic 
sublimate, and his materials proved very good for the study 
of those internal cavities, which remained very wide and distinct. 
Some larvae of C. planei which he obtaimed at Naples on 
March 25-7, 1898, labelled as fixed with acetic sublimate, are 
in a precisely similar condition to his material of C. echinata. 
Ludwig (22, p. 604) doubted the wisdom of Selenka’s 
employment of chrom-osmic mixture, and recommended a careful 
alcohol method. For observations on calcareous deposits in some- 
what advanced larvae the latter were simply killed in alcohol. 
For the orientation of the material to be sectioned, the 
double embedding in celloidin-paraffin gave good results. First, 
the material was put in celloidin-clove-oil mixture, and then 
hardened with chloroform. The hardened block was then 
clarified with carbol-xylol and transferred into melted paraffin. 
Even by employing the celloidin-paraffin method of sectioning, 
shrinkage of the material by about at least 15 per cent. diameter 
is unavoidable. That is why the Text-fig. 5, which is drawn 
from a whole mount, is larger than other figures obtained from 
sections. Sections were cut of a thickness of 5, except in the 
case of the ege and quite advanced young, which were cut 
into sections 8 p» thick. 
