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Recent Progress in our Knowledge of 
envelope was so opaque that no view could be obtained through it 
of the included structures, and in order to arrive at any knowledge 
of these it was necessary to rupture it. The nucleus thus liberated 
was found to have still further increased in length, and to have 
become wound into a convoluted and complicated knot. Along 
with the nucleus were expelled multitudes of very minute corpuscles 
with active Brownian movements. 
In a still further stage the nucleus had become irregularly 
branched, and at the same time somewhat thicker and of a softer 
consistence; and finally, it had become broken up into spherical 
fragments, each with an included corpuscle resembling a true cell 
nucleus in which the place of a nucleolus was taken by a cluster of 
minute granules. 
In this case the original nucleus of the Vorticellidan had thus 
become broken up into bodies identical with the so-called eggs of 
Balbiani, but this was unaccompanied by any conjugation or by the 
formation of anything which could be compared to spermatozoal 
filaments. 
What I believe we may regard as now established in the 
phenomena of reproduction in the Infusoria is, that besides the 
ordinary reproduction by spontaneous fission of the entire body, 
the nucleus at certain periods, and after more or less change of 
form has occurred in the Infusorium body, becomes broken up into 
fragments, each including a corpuscle resembling a true cell- 
nucleus; and that this takes place without necessarily requiring 
the influence of conjugation or the action of spermatozoa ; that 
these fragments after their liberation from the body of the In- 
fusorium become developed — still without the necessity of spermatic 
influence — directly or indirectly into the adult form. 
Whether proper sexual elements ever take part in the life 
history of the Infusoria remains an open question. 
Everts * has given an account of observations which, with the 
view of testing the statements of Greeff, he made on Vorticella 
nebulifera. Greeff, as we have seen, followed Claparede and 
Lachmann in attributing to the Vorticellae a true coelenterate 
structure ; and Everts, by his own investigations, has convinced 
himself of the untenableness of this view, and has been led to 
regard the Vorticellae as strictly unicellular. 
He recognizes the distinction between the cortical layer (which 
forms not only the periphery of the body but the whole of the 
stalk on which this is supported), and the central mass in which 
the nutriment is deposited, collected into pellets, and digested ; but 
instead of regarding this central mass as chyme, he looks upon it 
as an integral constituent of the entire body, like the central 
* Everts, Untersucbungen an Vorticella nebulifera. Sitzungsberichte der 
Physikalisch-Medicinischen Societat zu Erlangen. 1873. 
