Development of the Ovum. By W. II. Ballinger dc J. Dnjsdale. 93 
lias a real existence is shown in the result ; each auxospore 
forming a stem ancestor of a new series. 
This is what Biitschli extends to the Infusoria, and contrary to 
the interpretations of Balbiani, Stein, and others, maintains that 
the act of conjugation so well known amongst the Paramaecia, Vor- 
ticellae, &c., is not a precursor of sexual products, but simply a 
means by which these forms, exhausted by continued fission, become 
more highly vitalized and rejuvenated, and again enter upon the 
process of fissiparous multiplication, which indeed becomes thus 
their only method of increase. 
It should be noted that on the whole the facts adduced by 
Balbiani and Stein are admitted, but they are submitted to a 
wholly different interpretation ; and it is specially insisted on that 
the forms that go into the conjugation state are of a minimum 
size ; which fact Balbiani explains as the result of a special 
development for sexual purposes, but this is disallowed by Biitschli, 
who insists that it results from exhaustion of vitality at the ter- 
minus of a series of fissiparous multiplications. Indeed, these weak- 
ened and minimized forms unite in conjugation and are neither 
absorbed into each other nor produce embryos, but increase in size 
and vitality, separate, and commence again the fission by which 
alone increase is effected. 
The truth of this is insisted on as deriving strong support from 
some of the very remarkable external changes which the author 
has seen certain of the Infusoria undergo. In Euplotes and 
Oxytrichineae a great part of the ciliary system is said to perish 
towards the end of conjugation ; and afterwards, when separation 
takes place, to be again renewed. In Golpidium colpoda the 
entire mouth was lost in conjugation, but was renewed again after 
separation. So in Bursaria truncatella, the conjugated animals, it 
is affirmed, lose entirely the complex apparatus of the peristoma, 
which by a new growth after conjugation is restored. - So also 
there is declared to be a complete rejuvenescence of the more 
important internal parts. The ‘ £ secondary nucleus ” in Styloni- 
chia mytilus, and in Blepharisma laterita and Golpidium, colpoda 
the old nucleus is said to be eliminated and a new one formed. In 
others, part of the nucleus is thrown off, and part renewed ; in 
others a new nucleus formed and coalesced with the old one. 
From these and similar observations it is inferred that the “essence 
of conjugation consists in the rejuvenescence of both the indivi- 
duals ; ” and that this is chiefly centred in the “ secondary nucleus ’’ 
which is declared to be of the utmost importance in the life of the 
creature. 
During the process of conjugation, also, the plasma contents of 
the individuals have been seen to interchange ; this especially in 
Oxytrichineae, but also in other Infusoria. 
h 2 
