ON THE HISTOLOGY OF THE PEDICELLARIZ. 391 
transverse muscles, which, unlike the same muscles in the two varieties of 
pedicellarize just discussed, do not appear to show any striation, On one side 
below the muscles are a number of small circular bodies (a), the nature of 
which we have been unable to determine. 
Fig. 11 is a section taken higher up, about the middle of the head. The 
structure is almost identical with that of the section just described, but there 
is no special thickening of the outer epithelium, and the problematical bodies 
(a) are absent. 
Fig. 12 is a section taken near the top. Each of the glandular masses has 
become double, the division being foreshadowed in the lower part of the glands 
by their kidney-shaped outline in transverse section. The layer of fine mus- 
cular fibres is continued round each of the halves of the divided gland, between 
which is seen the section of the rod-like upper end of the calcareous valve ; it 
is triangular in section, and hollow. 
By teasing these pedicellariz, the existence of the three plates of elastic 
tissue, which were described in the ophiocephalous and tridactyle pedicellariz, 
was proved, but again, as in the case of the tridactyle pedicellariz, with con- 
siderable difficulty, as they are here very fine and delicate (fig. 5). We did not 
succeed in seeing them in any of the sections. The muscular fibres of the 
stalk, as described above, are in direct attachment to the bases of the cal- 
careous valves, and show none of the looped elastic fibres which form their 
termination in the ophiocephalous and tridactyle pedicellariz. 
Fig. 2 represents one of the calcareous valves, with its attached glandular 
mass separated from the other two, and viewed with its inner surface upper- 
most. The glandular mass is concealed by the fine muscular fibres which 
surround it. Lying on the calcareous valve, are about one-third of the way 
down the lower expanded portion, is seen a rounded body (a), which looks 
like a small gland. 
Fig. 9 represents the whole of the head of one of these pedicellariz pressed 
out and viewed from above. 
The three muscular masses which form the approximator muscles of these 
pedicellariz contain fibres which, as stated above, do not show any striation 
when treated with any reagents whatsoever, but under certain conditions they 
become swollen and spindle-shaped, as also do the transverse muscles of the 
ophiocephalous and tridactyle pedicellariz. These two conditions of the trans- 
verse muscles of the gemmiform pedicellariz are shown in Pl. XXI. fig. 3. 
Fig. 4 shows a few of the fibres which surround the central glandular masses of 
the pedicellariz very highly magnified. 
It is possible that these gemmiform pedicellariz have an urticating function. 
Mr SiApEN™~ has, in a paper already alluded to, published an account of these 
* SLADEN, Joc. cit. 
VOLieXX X.PART I. a0 
