Histology and Embryology . By G. S. Minot. 97 
given us by Biitschli led without exception up to it. Biitschli even 
admits that this process of fusion may happen, but be simply 
dismisses it as a “ very unusual one” — surely all the more important 
on this account, inasmuch as we know that in more highly organ- 
ized creatures not only a long time, but generations may intervene 
between distinct acts of fertilization. 
2. It does not follow that if rejuvenescence be rejected to the 
extent and with the meaning Biitschli gives it, that it must be 
rejected altogether. He gives us many remarkable facts that 
deserve further experiment and research ; and it may result, that 
what he calls rejuvenescence, is one of the many modes by which 
rapidity of fissiparous multiplication is in some organisms aided, 
and the necessity for the true act of fertilization is made less 
frequent ; and 
3. It is clear that there are points in the theory of Balbiani 
which the facts given by Biitschli overturn ; while there are others 
that certainly remain unshaken, if they be not strengthened. But 
it is needful to remember that if the facts given by Biitschli wholly 
invalidated the interpretations of Balbiani, the theory advanced by 
Biitschli by no means follows as a consequence. In the present 
state of this inquiry we must seek facts industriously, and with 
persistent honesty, and be assured that their accumulation will lead 
to important issues ; but we shall do well to place theory, however 
fascinating, in an extremely subordinate place. 
Y . — German Methods in Histology and Embryology. 
By Charles Sedgwick Minot. 
The use of the microscope goes hand in hand with the work of 
zoologists in Germany, and it is there that we find the greatest 
number of means employed to render the objects suitable for exa- 
mination. I have frequently heard American zoologists express a 
slight distrust of histological methods — well founded, perhaps ; it 
ought not to lead to the rejection of the benefits to be obtained 
from using them, but merely to greater caution in employing 
them. 
It is well known that animal tissues and organs consist of cells 
of various kinds, variously grouped together. The forms which 
these cells can assume lead to the most curious transformations, so 
that things as different from one another as muscular fibres, blood- 
corpuscles, and ganglion-cells can be traced as modifications of the 
same primitive form. The work of microscopic anatomists is to 
detect the changes which the simple cells of embryos undergo in 
