148 Barber — The Structure of P achy theca. II. 
B 1 ,2, and 6 to determine the correspondence of the rounded 
inner ends of the spaces with the oval bodies of these figures. 
Internally to the zone of oval bodies a clear, yellowish or 
brownish layer, of some thickness, lines the whole inner sur- 
face of the specimen. It will be seen from the figures that 
the cortical tubes are immediately continuous with this layer, 
and arise directly from it as so many radiating processes. 
The inner margin of this medullary 'portion frequently presents 
circular or cylindrical forms, such as would be obtained by 
transverse or longitudinal optical sections of tubular cells; 
but all, or nearly all, traces of vegetable structure have dis- 
appeared, and these portions, and all other parts of the prepara- 
tion, appear at present in the form of a mineral concretion 
around a framework of cells whose outlines have disappeared. 
Slide 2 (Figs. 2, 2 a) bears a tangential section through 
the other half of the same specimen, in a plane at right angles 
to that of section 1. 
The centre of the preparation is composed of the transverse 
sections of well-marked circular tubes, with thick walls and 
broken contents, separated from one another by a clear 
yellow matrix ; in fact, it presents exactly the opposite 
appearance to what would have been expected from an ex- 
amination of Slide 1. 
As seen in the figure (2), however, as the centre of the 
preparation is left, and the tubes are cut more and more 
obliquely, anastomosis of these takes place ; while the outer 
part of the section shows a state of things the reverse of that 
at the centre, namely, the presence of a series of more or less 
obliquely cut clear yellow tubes separated by a broken, dark- 
coloured matrix. 
An examination with the high power reveals the following 
facts (Fig. 2 a). Each of the central tubes has a beauti- 
fully defined wall of uniform and considerable thickness ; and 
this wall is marked by perfectly regular parallel striae at 
right angles to its surface. The contents are more or less 
broken up, either showing holes, or being filled up by clear 
yellow crystals or a dark-brown granular mass. 
