CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 521 
pletes the series in a more satisfactory manner since its division is 
posterior to the pharynx and in exactly the same place as (1) and 
On reviewing the accounts of these authors (Zacharias, ’86; 
Kennel, ’88; Sekera, ’88; von Graff, ’99, and others), one finds 
nowhere given a complete description with adequate figures of 
either the external or the internal changes from day to day in a 
normally divided Triclad. The external changes have been quite 
well described by Kennel (’88) in the single case of Planaria fissi- 
para^ which is a different type from Plcmaria maculata, and some 
of the papers reviewed by von Graff (’99) seem to have indicated 
pretty well the simple external changes of the land Planaria. The 
histological changes connected with normal fission have been quite 
generally neglected. Although Keller (’94) mentions them as simi¬ 
lar to those following the regeneration after artificial mutilation, he 
gives no figures of the process and seems to have studied mainlj^ the 
regeneration after artificial cutting. The occurrence of fission in 
P. maculata was first noted by Miss Randolph (’97) in a paper upon 
the regeneration of this form. This is, however, only a brief mention 
and there is no attempt at a detailed description. As so much study 
is being devoted to the regeneration of planarians after artificial 
mutilation, it seemed to me worth while to offer a thorough descrip¬ 
tion of every phase I could observe of the normal fission and sub- 
l^equent regeneration of P. maculata^ and this is embodied in the 
following. 
If previous to the normal fission of Planaria maculata there is 
any external furrow to indicate the place of division, it can last but 
a very short time, for many of my specimens divided within a few 
minutes after I had scrutinized them very closely for some trace of 
a furrow and found none. This is illustrated by figure 22, of plate 
10, a whole specimen which was found divided (pi. 11, figs. 24, 25) 
soon after it was drawn. I believe, therefore, that the single case 
where I saw the actual separation was the normal process. In this 
case the worm, just after being transferred upon a spatula from one 
dish to another, pinched itself in two apparently by a quick muscu¬ 
lar contraction. There was nothing more to the process (pi. 10, 
fig. 22; 2^1. 11, figs. 24, 25). The two pieces moved away without 
inconvenience and were exactly alike all other newly divided pieces 
found in the ponds or the laboratory (pi. 9, fig. 2; pi. 10, fig. 19). 
