COHN, ON NASSULA ELEGANS. 97 
of the last summer I had an opportunity of ascertaining 
the existence, besides some incompletely observed instances, 
of a decided, though peculiarly modified case of embryo- 
formation, in the interesting Infusorium described by 
Ehrenberg as Nassula elegans. 
I found this rare animalcule at the same time with 
Ophryoglena atra and Bursaria truncatella, \ately investi- 
gated by Lieberkiihn. In form it resembles Paramecium 
Aurelia, though rather narrower, ard, like Paramecium, it is 
surrounded with a lattice-marked cuticle, supporting the cilia 
which are uniformly distributed over the surface. The in- 
terior of the animal presents yellowish-brown and _ violet- 
eoloured pigment-masses, which are sometimes few in num- 
ber and isolated, and at others aggregated into masses, and so 
numerous as to fill the entire body. At the posterior part 
of the animal, near the anal orifice, is situated a large violet- 
coloured substance, which appears to be rendered of a deeper 
colour from the presence of imnumerable dark-blue granules. 
And occasionally a similar substance may be observed at the 
opposite end of the body. Various opmions have been en- 
tertained with respect to the nature of these masses. Hhren- 
berg refers them to a class of bodies, the knowledge of which 
has suddenly thrown a clear light upon many hitherto 
obscure and doubtful points; he sees in them, in fact, a 
special system, destined for the secretion of a violet-coloured 
juice, visibly subservient to digestion, and therefore of a 
biliary character. He describes an aggregation of beautiful 
violet-coloured vesicles on the back of the animal, from 
which is prolonged a series of violet or clear and colourless 
vesicles along the dorsal region towards the anus. The 
mixture of the coloured secretion with the contents of the 
gastric cells, takes place in the posterior third of the body ; and 
both are expelled at the same time. I am not, myself, as yet 
quite clear as to the nature of these pigment-masses; though 
it seems to me scarcely to admit of doubt that they belong to 
that class of colouring matters met with so extensively in 
the microscopical Algz, and more especially in the Oscilla- 
rine and Nostochinez, and named by Nageli phycochrom. 
The characteristic property of this colouring matter re- 
sides in the circumstance, that either in the course of the 
vital processes, or during the decomposition of the tissues, it 
undergoes various changes of hue, such as into bright-green, 
indigo-blue, violet, purple-red, olive-green, and brownish-yel- 
low. Among the Oscillatorie we meet with species exhibit- 
ing all these modifications of the phycochrom. It is a pe- 
cuharity also of this material, that in the living plant it 
