STUDIES IN SPICULE FORMATION. 285 
cell. It is also shown that spicules situated in different 
portions of the colony (and so subject to different environ- 
mental influences) are different in form—spicules situated 
near the surface being monaxon and unbranched, spicules 
more deeply situated being more or less branched and 
irregular. 
Kowalevsky and Marion (8) in 1883 confirmed Koch s 
statements as to the intra-cellular growth of Alcyonarian 
spicules, although they gave no figures in support of their 
statements. 
In 1892 K. C. M. Schneider (4), in a very short paper, and 
also without giving any figures to justify his statements, 
asserted that in development the scleroblast gradually 
assumed the form of the adult spicule, which latter was 
then produced by the calcification of the cell-substance. As 
Hickson (5) remarks, the appearance of developing spicules 
does not by any means justify this assertion, and it is, 
moreover, grossly improbable that the actual protoplasm 
should become converted into the crystalline substance of 
the skeleton. 
In 1899 G. C. Bourne (6) made some observations on the 
formation of the spicules in Alcyonium digitatum and 
Gorgonia cavolinii preparatory to investigating the 
minute structure of the Madreporarian corallum, and, 
although only incidentally made, these observations of 
Bourne up to the present afford the most complete account 
of the subject extant. 
In the following lines I shall occasionally have to refer to 
certain of the statements made by Bourne and less often by 
Hickson. 
PRELIMINARY RemArRKs: MetHops oF PREPARATION, 
HIstToLoGy, ETC. 
Bourne’s method of preparing microscopic specimens of 
Alcyonium digitatum for examination of the developing 
