68 
conclusion that P. oblonga is widely separated by its cha- 
racters from P. lactea, the two most prominent of these 
characters being the erect oblong segments all extending 
to the base of the shell, and the inverted tube at the mouth. 
With regard to P. Orbignii, the exhibited specimens of 
which were P. gibba with the peculiar wild-grown last 
chamber, he still thought his formerly expressed opinion 
(Memoirs Lit. and Phil. Soc., Manchester, vol. 8, third series, 
1866-67) was correct, namely, that the formation of an ir- 
regular shell-covering over the external sarcode in two or 
three broad arched passages with numerous tubes for the 
protrusion of pseudo -podia, was due to failing power in the 
animal owing to advanced age. In P. gibba the most 
clearly expressed idea in the structure is strength, and 
ability to resist rough usage, as is seen both in the rounded 
pebble-like shape, and in the absorption of the interior walls 
with redeposit of the shell-matter on the exterior ; and it 
would seem that the best proof of vigour in the animal is 
the regular formation of successive chambers on this globu- 
lar plan ; requiring, as in other regular foraminifera, an 
active contraction and collection of the external sarcode 
into the correct shape and position to form each new cham- 
ber; whilst neglect to do this, until a shell-covering has 
formed upon it, in a shape the least capable of resisting in- 
jury, can scarcely be referred to anything but enfeebled 
vital power. 
