CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 519 
The fact that all the specimens collected from a sexual locality 
are found each fall with reproductive organs developing, shows that 
this species becomes sexually mature the year after hatching, 
whereas Ijima (’84) found that the young of Dendrocoehim 
lacteum did not develop any reproductive organs until the second 
year. Planaria simplissima^ which I followed through the fall 
and winter at Williamstown, Mass., (;00a) showed exclusively 
sexual individuals during that time. The ovaries and testes were at 
first found in their younger stages, but in the early spring they were 
so far developed as to indicate the nearness of the sexual season. 
It is therefore probable that this form also develops its reproductive 
organs the first year. 
The Act of Normal Fissiox axd the External Changes 
F OLLOWING. 
Jacob Keller (’94), in an article based upon the investigation 
of normal fission in rhabdocoele Turbellaria (Stenostoma and 
Microstomum) and the regeneration of fresh-water planarians, has 
tabulated the various modes of normal fission in Triclads and 
Rhabdocoeles. This and his review of the literature make anv such 
«/ 
attempt on my part unnecessary. I will merely indicate the schema 
of the types of fission according to Keller and the place in this 
which the type found in Planaria maaulata occupies. He divides 
the normal fission of Triclads into two types: (1) that in which 
the new organs develop previous to the separation of the new 
formed individuals {^Planaria fissipara^ Kennel, ’88) and (2) that 
in which the development does not begin until after the new indi¬ 
viduals have separated (various land planarians and Planaria 
albissima, Sekera, ’88). Such a distinction is not hard and fast, 
because the process in Planaria subtentaculata (Zacharias, ’86) is 
somewhere between these two conditions. The first type is similar 
to the fission which occurs in many Rhabdocoeles ; the second is in 
some cases a simple fragmentation and with difticulty distinguished 
from the regeneration following accidental mutilation. Planaria 
maciilata supplies just the type of fission necessary to make a very 
complete series from the one extreme to the other. Briefly, this 
series is as follows : — 
1. In the normal fission of P. fissipara (Kennel, ’88), a con- 
