284 W. WOODLAND. 
their various forms and a detailed account of their structure, 
but did not investigate their development. According to 
Kolliker, an Aleyonarian spicule consists of an organic and 
an inorganic part, the former, constituting the bulk of the 
spicule, being crystalline in nature and with a complicated 
structure, the latter consisting merely of a cuticular spicule 
sheath. Kolliker thus denied the existence of one of the 
most conspicuous features of this type of spicule, viz. the 
large central organic axis; this, however, is not surprising 
since he also failed to observe the still more conspicuous fact 
ot the enclosure of these spicules within a well-defined proto- 
plasmic layer containing granules and one or more nuclei, 
and therefore of their intra-cellular origin. Nevertheless, 
many of Kolliker’s observations on the more intimate struc- 
ture of the Alcyonarian spicule are correct, as instance, e. g. 
his statements as to the concentric lamellar structure of the 
spicule body when seen in transverse section, the breaking 
up of the spicule into smaller crystalline elements on treat- 
ment with weak acids, and the ‘‘axial” continuity of the 
processes of the spicule with the main trunk, resembling, as 
Bourne remarks, the origin of secondary roots in a plant. 
G. von Koch (2) was the next investigator who contributed 
to our knowledge of Alcyonarian spicules. He ascertained 
to some extent, and for the first time, the development of the 
spicules in Clavularia prolifera, giving in his paper on 
the histology of this species highly-coloured figures of the 
earliest stages of spicule formation and of the subsequent 
growth. He rightly insisted on the endoplastic development 
of the spicules, showing that these not only originate in 
scleroblasts derived from the ectoderm, but remain con- 
spicuously enveloped by the cell-substance throughout their 
existence. Koch’s figures show well the presence of nuclei— 
never exceeding two in number it is important to note—in 
the granular protoplasmic layer investing the spicule, and 
also incidentally prove that the change in shape of the spicule 
from the spherical to the elongated is strictly correlated with 
the division into two of the nucleus of the original mother- 
