STUDIES IN SPICULE FORMATION. 535 
of alcohol being made up with absolute alcohol and distilled 
water to ensure complete neutrality—a precaution most 
essential to observe in the case of all reagents employed). 
Before staining in picro-carmiue, each Cucumaria was cut in 
half longitudinally with a pair of scissors and the internal 
viscera and musculature on the inner side of the body-wall 
removed, the whole of the latter being carefully scraped away 
with a scalpel. From absolute alcohol the Cucumarias were 
then transferred to a saturated solution of lichtgriin!in absolute 
alcohol, in which they were left fora quarter of an hour, then 
washed in absolute alcohol, cleared in xylol, and finally 
mounted in Canada balsam, usually with the inner side of the 
body-wall placed upwards on the slide. The body-wall must 
be well flattened out on the slide before covering with the 
cover-slip (each Cucumaria should be cut into at least four 
pieces), and a lead weight placed on the cover-slip after 
covering until the balsam is fairly dry, which condition is 
seldom obtained under aweek. In studying the small super- 
ficial spicules of the Cucumaria, the body-wall, of course, 
must be placed outer side uppermost on the slide. 
The structure of the body-wall of the Cucumariide having 
been already well described in several of the larger text- 
books and papers dealing with this subject, such as those by 
Hérouard, there is no need for me to here re-describe it; it 
will suffice if I briefly mention the several kinds of spicules 
to be found in the two species of Cucumaria which I have 
studied — Cucumaria sp. and C. brunnea;?—and the 
1 In the plates a grey tint has been substituted for green. 
2 Of these two (possibly three) species of Cucumaria, I received from 
Plymouth at least one dozen specimens of C. sp., and six or seven of what I 
have called C. brunnea. Concerning the identity of this latter species I 
am tolerably certain that most of my specimens of it were brunnea, both on 
Mr. Pace’s authority and on account of the external appearance (possibly, 
however, one or more C. saxicola were also examined with C. brunnea 
as possessing no nodulated spicules). But with regard to the identity of the 
species of which I received by far the larger number of specimens I am very 
uncertain. Though, as just stated, the greater number of the Cucumarias I 
received from Plymouth was of this species, yet, curiously enough, on 
