92 Development of the Ovum. By W. II. Dallinger & J. Drysdale. 
nomena manifest at different periods, the intervals between which 
are blank. Further, whilst the use of reagents on the dead forms 
taken at various stages is of the utmost value, when they are exa- 
mined side by side with continuous observation on the living form, 
these may be not only not instructive, but misleading when taken 
by themselves. 
Butschli’s observations are numerous and interesting, but their 
value will he best estimated by understanding briefly the nature 
of the hypothesis they are declared by their author to indicate. 
Put in its shortest form, it is that conjugation amongst the Infu- 
soria is simply a rejuvmescence of the creatures which undergo it, 
enabling them to become “ the stem ancestors of a series of gene- 
rations ” which propagate by fission. As yet the process of rejuve- 
nescence has had, in biology, a limited application, being noticed 
in the formation of the swarm- spores of (Edogonium and other of 
the lowliest plants ; but its connection with sexual reproduction 
is not clear, as no union of different elements has been made out, 
and it is by no means certain that the whole process of repro- 
duction is exhausted by it. When, however, it is combined with 
conjugation, as in the Bacillariaceae, it becomes plainer ; although, 
so far as is known at present, it by no means follows that the whole 
generative process in these forms is known ; but it is to the Aux- 
ospores by which rejuvenescence is secured in these forms that 
Biitschli appeals for the support of his theory of infusorial con- 
jugation. Pfitzer and Schmitz have made what are at present the 
most complete observations of the phenomena in question ; from 
which we learn that the customary mode of reproduction is by 
fission, but at each repetition the individuals dwindle in size, until 
they can apparently go no farther,* then the conjugation of two 
individuals takes place, the formation of auxospores being the 
result, that is to say rejuvenated individuals ; and from these a new 
departure of fissiparous generations takes place, well observed by 
Schmitz in the case of Gocconema cistula. There is no coalescence ; 
the frustules simply lay themselves parallel to one another, they 
become surrounded by a common envelope of mucus; the pro- 
toplasm of the cells comes into contact, each frustule grows larger 
and becomes an auxospore. What the influence is which these 
frustules exert upon each other is wholly unknown ; but that it 
*■ It is impossible not to notice here the extremely interesting and certainly 
somewhat remarkable paper of Dr. Wallich in the February number of the 
‘ Monthly Microscopical Journal’ for 1877, “ On the Relation between the Deve- 
lopment, Reproduction, and Markings of the Diatoinacese;” for in this paper 
what is apparently the auxospore of Pfitzer and Schmitz is called the sporangia l 
frustule. But this, instead of having dwindled in size before conjugation, appears 
to have become enormous in proportion, and within this the “ new parents of the 
race arise,” and from the conjugation of these the new forms spring as daughter 
frustules. 
