932 The Avierkan Naturalist. [October, 
lytic disintegration and total resorption within the uterine coruna, even 
after an advanced stage of development has been reached. Dr. Arthur 
V. Meigs has shown me a series of fine preparations showing such a 
process, and one of my pupils, Mr. Edward Bancroft, has prepared a 
series of sections from the uterus of a mouse showing much earlier 
abortive stages of the embryo, which also indicate that absorption 
takes place subsequently. 
These facts indicate that the fertility of an individual may be re- 
duced by processes of absorption of the whole embryo within the 
uterus. These phenomena may be associated with the resorption of 
ova in the ovary, as described by Ruge, to which I can add that such 
a process of resorption of ova is a common occurrence at the end of 
the spawning season in the ovary of common sturgeon. These facts 
further indicate how complex the physiological factors are which de- 
termine the size and number of the ova matured by a species dunng a 
single season. They also go far toward showing how important it is to 
consider the effect of the acquisition of certain habits upon the result, 
such as those of copulation, nidification, stealth, and care in hiding 
the ova, the latter often being retained for a greater or lesser period of 
time, until it is convenient or safe to deposit them. . 
Finally, it may be affirmed that the solution of the question of rela- 
tive fertility of a species, the acquisition and loss of a food-yolk, is 
completely beyond the reach of the current ''Ding an Sich'' morpholo- 
gical method. It is also clear that the neglect to study the reproduc- 
tive habits of a species in connection with its physiological and mor- 
phological characteristics is to be condemned. Unless the contrary 
method is followed, there is no possible clue to the origin of the cal- 
careous egg-shell in the ova of oviparous land vertebrates. There is, 
moreover, otherwise no hope of connecting the phenomena of ova- 
gestation with those of utero-gestation ; the one must have preceded 
the other, otherwise the remarkable fact that no well-authenticated case 
of placentation has ever been made out where there is a large amount of 
yolk present, also loses its obvious significance, while the development 
of an outer layer of nutritive epiblast in mammals (trophoblast of 
Hubrecht, Deckschicht of other authors) loses its adaptive import and 
becomes a mere morphological ''Ding an Sich,'' to be shelved and 
labeled like a rare bon mot in the mental cabinet of the specialist. 
It may be added, in conclusion, that the membrana putaminisoi eggs 
of birds and reptiles is a reticular but cuticular membrane, which is 
to be regarded as the homologue of the keratose cuticular secondary 
