390 A. A. W. HUBRECHT. 
a very ominous confession. And it seems to me to be appro- 
priate to limit the use of the name “ decidua ’’—as I have done 
in this memoir—and to confine it to the hypertrophied pro- 
liferating region of the mucous membrane of the uterus, in 
which these proliferations make their first appearance in the 
preparatory stages of pregnancy. 
The formation of the decidua menstrualis has more and 
more definitely been shown to be one and the same process, 
and all monodelphous mammals are deciduate in this sense that 
a special activity in the maternal mucosa precedes or coincides 
with the fixation of the embryo. And so the source of the 
possible confusion above alluded to is the very term “ decidua.” 
It was used since olden times for a portion of the uterine 
mucosa, whereas the adjective “ deciduate” as applied by 
Huxley referred to the character of the maternal placenta. As 
the maternal placenta is always formed out of decidual 
tissue, it was misleading to call it “ deciduate” or “ non- 
deciduate” according to the bare fact of its being shed at 
parturition or not. If the old name of von Bar and Eschricht, 
“‘caducous or non-caducous,’”? had been adhered to, no mis- 
understanding would have arisen. A very telling proof of the 
confusion to which this nomenclature necessarily leads is, for 
example, the distinction insisted upon by Rolleston, and also 
recognised by Turner (‘ Phil. Trans.,’ vol. clxix, p. 562), of a 
deciduous and a non-deciduous [decidua] serotina. The word 
decidua in brackets, which is inserted by me, has reference to 
the modified condition of the maternal mucosa, in which we 
distinguish in man and the Primates the three regions : decidua 
serotina, d. vera, and d. reflexa. Its combination with 
homonymous adjectives gives offence because of the different 
meaning which is there attached to the term deciduous. It 
is evident that it would be more harmless to speak of a 
“‘caducous and a non-caducous serotina.” Ercolani’s extensive 
labours are to a certain extent the outcome of this misunder- 
standing, and, with respect to classification and nomenclature, 
a reaction in the right direction, though perhaps too cumbrous 
to have been convincing. 
