STUDIES IN SPICULE FORMATION, 307 
lisation of nineteen weeks, i.e. 133 days—whereas in 
MacBride’s experience, metamorphosis occurred about the 
fiftieth day. This abnormal prolongation of the larval stage 
was, without doubt, due to the fact that pressure of work at 
the laboratory prevented very much attention being bestowed 
upon the larve during the summer months—the somewhat 
stale water and scarcity of food resulting from this inattention 
retarding the normal rate of development ; however, by Sep- 
tember 12th all the plutei had undergone metamorphosis, and 
one jar alone contained “ quite a hundred” small Echinus. 
As might have been expected, most of these died later through 
sheer lack of food, and by December 12th only four Hchinus 
were left. Had it been possible to properly superintend the 
later development of these specimens, I have no doubt but 
that they would have attained a very considerable size before 
succumbing to laboratory conditions of life. 
The only method of efficiently preserving the plutei at 
different stages of development—the desideratum, of course, 
being the preservation of the skeleton—which I found prac- 
ticable was as follows:—A dozen or more larve were removed 
from one of the large bell-jars employed by means of a small 
pipette (the Browne plunger having, for the purpose of col- 
lecting, previously been removed for about half an hour or 
less to enable the larve to aggregate in the upper layers of 
water), and placed ina test-tube. ‘The problem now was to 
get rid of the great bulk of the water in which the dozen or 
more larve were suspended, and this was easily solved by 
means of an ordinary centrifuge—the larve settling at the 
bottom of the tube, and so allowing all but one or two drops 
of the water to be poured off. The test-tube was then filled 
with absolute alcohol, and this was usually a sufficient quan- 
tity to render negligible the small volume of sea water origin- 
ally present; when, as occasionally happened, the mixture 
thus formed contained a conspicuous precipitate of calcium 
sulphate, the centrifuge was again used. The larve being 
1 T understand that two of these Echinus were still living in August of 
the present year (1905), and were about as large as walnuts. 
