2Ows FORMATION OF SHELLS OF ANIMALS, ETC., 
sufficiently advanced to give them the elliptical form. 
Besides these there are others representing intermediate 
stages. On examining specimens similar to the one of 
‘which this is a drawing, a difference of structure between 
the central and peripheral part in such globules (0), 
especially on the side where they are in apposition, is 
distinctly visible by polarized light, under which these 
parts appear of different colours. And, during their 
further coalescence, the central portions appear to join 
before the peripheral ones; and, at a stage still more ad- 
vanced, the central portions of the two spherules will be 
seen to have coalesced sufficiently to circumscribe a per- 
fectly elliptical area, whilst the peripheral parts, retaining 
more of their spherical form, present a depression all 
around their line of contact ; or, in other words, the dumb- 
bell figure is retamed longer by the outer than by the 
inner portions. This want of correspondence in shape of 
these two parts proves that the central elliptical portion 
cannot have acted as the nucleus upon which the circum- 
ferential one was moulded. (See fig. 2 6 and 6.) It will 
not be difficult to account for this fact on the supposition 
of its being a necessary effect of attraction. Indeed, it 
seems to me that the fact will do as much towards proving 
the reality of the principles adduced to account for it as 
any application of these principles can do towards showing 
the nature and cause of the fact; or, m other words, the 
fact explains itself. A few observations, however, may 
make the subject more clear. For it will be evident, on the 
mere inspection of the particles (0, 6’), and the illustrative 
diagram a, B, C, D, fig. 2, that as the molecules occupying 
the outer portions of the remote hemispheres preserve their 
spherical form not perceptibly altered, they have the same 
arrangement in respect to the centres of the coalescing 
