516 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The Life History of Planaria maculata in Different 
Localities. 
With a single exception, all the Triclads which I have found 
described as reproducing asexually, are without reproductive organs 
during the period of fission. The one exception is the land plana- 
rian Placocephalus semperi mentioned by von Graff (’99, p. 224). 
There is also to my knowledge but a single exception to this in 
the Rhabdocoeles, viz., Microstomum (Sekera, ’88). Since all 
planarians for a long time after hatching remain without these 
organs, it might easily be supposed that it was during this post- 
ernbryonic period that the asexual reproduction occurred. In a 
hypothetical case we might suppose the young hatched in the spring 
and early summer, and from then until the fall there might be more 
or less asexual reproduction. In the fall this ceases and the repro¬ 
ductive organs make their appearance. After the egg laying in the 
following spring the adults might die or they might lose their 
reproductive organs and live on. In the latter case they would at 
the end of the summer be indistinguishable from the young of that 
3 ^ear. If it could be proved that the adults all die after their egg 
laying, i. e., live but one year, we should then have a kind of 
alternation of generations in which all the individuals resulting 
from the sexual multiplication became sexually mature. If it could 
not be proved that all the old ones died off, we should have the 
possibility and even the probability that their reproductive organs 
disappeared and they again passed through a season of asexual 
reproduction with the younger worms. We should then represent 
the life history as made up of alternate periods of asexual and 
sexual reproduction. This would explain the entire absence of 
reproductive organs in all the worms of a locality at certain seasons 
and the abundant occurrence of normal fission. 
In one locality, where I have observed them for three years, 
Planaria maculata goes through some such series of changes as 
that I have just indicated, with the probability that the old ones 
live on after the egg laying. The point of interest is, that there 
seem to be different courses in different localities. I have taken 
systematic observations in a number of places during the past three 
years, the results of which can best be presented by a statement of 
the data obtained. I should preface this by saying that I have 
