518 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
In another locality which I have kept track of for one year there 
seems to be the same condition as in locality 1. 
These observations are based upon many more individuals than 
those I have been able to stain whole, or to section. The egg cap¬ 
sules remain upon »the stones for* three or four months after the 
young worms have broken from them and afford unmistakable evi¬ 
dence of the occurrence of a reproductive season even though no 
sexual worms are found. In like manner when the capsules have 
never been found, though the under sides of thousands of stones 
were examined in collecting and I was constantly looking for them, 
it amounts to a disproof of any extensive egg laying in a given sea¬ 
son, which alone wmuld be sufficient without the additional evidence 
obtained from the absence of reproductive organs in all the speci¬ 
mens examined. When worms have their reproductive organs even 
partially developed, the genital pore, can be readily seen on the ven¬ 
tral side, and as they approach sexual maturity the two vasa deferen- 
tia full of sperm are very noticeable ventrally as two white cords on 
either side of the pharynx. This makes it possible at the egg laying 
season to determine the presence or absence of reproductive organs 
in every specimen collected. These facts are familiar to every one 
who has studied planarians, but I mention them in order to show 
the number of specimens examined to furnish the basis for the state¬ 
ments regarding the presence or absence of the reproductive organs 
in the respective localities. 
As to the interpretation to be put upon these conflicting data : if 
I had only localities 2 and 4, the one with no evidence of fission, 
the other with no sign of sexual organs, I should conclude that there 
were two varieties of Plcmaria maculata, one of which reproduced 
almost entirely by fission and in which reproductive organs were 
very rarely found. Locality 1, however, shows that fission may 
occur in what I have termed a sexual locality, and locality 3 shows 
that an asexual locality may sometimes produce worms with sexual 
organs. The gradation which the four localities present, can, it 
seems to me, be explained by supposing that Plcmaria maculata^ 
having the power of reproducing itself by fission, which is common 
to many planarians, this mode of reproduction has been in some 
localities substituted almost entirely for the sexual method. Whether 
this substitution is permanent or only temporary can, of course, only 
be ascertained by observations extending over a number of years. 
