54 
PROCEEDINGS OF SOCIETIES. 
The Chairman said he had brought for the examination of the 
Fellows a specimen of petalody of the sepals of Gloxinia. Two por- 
tions of the cleft sepal instead of preserving their pointed shape had 
expanded and assumed the colour of the corolla. 
The Chairman again called the attention of the meeting to the 
diatoms exhibited in the room, which he thought would be found worth 
notice. Diatoms he thought might be broadly divided into two groups, 
one of which had more or less distinct rows of beads, and in which a 
fracture always occurred between the rows; and the other group might 
be described as belonging to the same type as the Coscinodiscus 
described by Mr. Stephenson and Mr. Stewart, and were composed of 
a beaded framew^ork with areolar depressions of different sizes. If 
one of the latter type were examined — say, for instance, Eujphodiscus 
Argus — with a good ^-inch objective, not too wide in angle of aperture, 
it would be found to be composed of a framework which was distinctly 
beaded, and which enclosed areolae. In some of the Californian forms 
on the table the fracture had taken place exactly in the way which 
Mr. Stephenson had indicated. He was inclined to think that the outer 
layer was in many cases perforated so that the water could get through 
to the layer below, at the same time it was very likely liquids could 
to some extent pass through a thin film of silica, and that a great 
deal of the nutrition might be taken in in that w^ay. 
Mr. Charles Stewart said there could be no doubt whatever that 
silex really was penetrated by water ; that which was deposited in the 
cavity of the bamboo was clearly so, and the same might be shown 
with respect to that which was found in the common cane. In the 
latter the cells presented a peculiar appearance when looked down 
upon, and showed a more or less pear-shaped cavity completely 
covered with silicious matter. 
Mr. Stewart then proceeded to describe two objects which he had 
brought for exhibition. The spines of the Echinodermata were for 
the most part very well known ; but there were some which he 
thought were much less known than the others, namely, those which 
were found only on a limited portion of the surface of the shell 
immediately surrounding the pentagonal opening on the under side, 
through which the teeth protruded. These spines were found on all 
the common Echini except the Cidaridae ; in size they were extremely 
minute, and seen as opaque objects they glittered like little diamonds, 
and in form they were shaped more or less like water bottles. The 
main mass of their structure was formed of solid calcareous matter 
deposited layer by layer; but it did not show any indication of a 
black cross under polarized light, as might naturally be expected, but 
simply polarized of uniform dull colour, showing that the actual tension 
was in one direction only ; and it was in reality as if a person had 
taken a piece of carbonate of lime and carved it into the shape of the 
spine. They had been spoken of by Louvain as the Spheridia. They 
were so few in number on some Mediterranean species as not to exceed 
five, though on the common British Echini as many as thirty and 
upwards might be found. 
In addition to these spines, he had also brought to the meeting 
