82 A. A. W. HUBRECHT. 
been made of the rich and varied material demonstrate the 
perfect care which most of my correspondents have bestowed 
on the preservation. Consequently the histological details 
of the placentation process, of the formation of the ger- 
minal layers, and of the ontogenesis can be studied from 
these preparations quite as satisfactorily as if the preparations 
had been freshly made in the laboratory. 
Again in this respect Kleinenberg’s mixture (picro-sulphuric 
acid) has proved to answer to a very high standard of excel- 
lence; in the case of the preservation of uteri in toto it gives 
the best chances for the finer details of early blastocysts therein 
enclosed, or of the placentary structures in the course of forma- 
tion, to be perfectly preserved ; always on this sole condition, 
on which I have everywhere laid particular stress, that the 
extirpation be made instantly after death. Preparations made 
from animals that had been dead even for only a very short 
time have already undergone so considerable an alteration that 
they are of very inferior value for comparative and especially 
for histological research. 
A point which had more particularly puzzled me before I 
commenced my peregrinations was the question at which 
period of the year the animals I was going to search for repro- 
duced their species. As was already noticed above, the litera- 
ture on the subject leaves us entirely in the dark with respect 
to this point. And though the alternation of seasons is much 
less marked in the tropics than in the temperate regions, still 
the regular succession of the “rainy” monsoon and of the 
‘‘ dry’? monsoon—more marked, however, in certain parts of the 
Archipelago than in others—might be expected to have a certain 
influence on the birth-rate and on the association of the sexes 
in these animals. 
If in the commencement I have been inclined to believe 
that it would be possible to detect any such parallelism, still, 
as the collections have increased, it has become more and more 
evident that reproduction of the species investigated occurs all 
the year round. 
In the same months the most divergent stages of pregnancy 
