CURTIS: LIFE HISTORY OF PLANARIA MACULATA. 527 
many as five. Where there are but two main branches the chauges 
are easily followed. As late as the third day, the anterior ends may 
remain separated (pi. 9, fig. 4), but usually on the third day they 
have met and fused together (pi. 9, fig. 16). During the third and 
fourth days this fusion has extended farther back (pi. 9, fig. 17). A 
small pharynx, not as yet connected with the gut, is visible on the 
fourth day in the live animal (pi. 9, figs. 5, 17). The fused rami 
make themselves over anteriorly into the single anterior gut ramu& 
of the Triclad with no apparent increase in the amount of tissue 
involved (pi. 9, figs. 5, 6, 17, 18). The new pharynx is connected 
Avith this posteriorly by the end of the fourth day. On the fifth day 
(pi. 9, figs. 6, 14) the pharynx may be protruded and used in feed¬ 
ing, though as yet quite small. In the tail pieces the phaiwnx 
develops somewhat anterior to its final position (pi. 9, figs. 6, 9). 
From the fifth day on, (pi. 9, fig. 6) the only change is the slow rear¬ 
rangement of the proportions as the pharynx moves back to its nor¬ 
mal position, or if the pharynx be taken as the fixed point the old 
tissue may be said to move around in front of it. This remodeling- 
of the contour is similar to that described in all studies of regenera¬ 
tion (Morgan, ’98, : 00; Bardeen, :01). 
As will be seen from the figures (pi. 9, figs. 2, 12, 13 ; pi. 10, fig. 
21; pi. 11, fig. 25) the portions of the gut found in tail pieces are- 
hardly the same in any two cases, but the same formation of a single 
ramus always follows when the several rami unite at their anterior 
ends (pi. 9, figs. 6, 14, 18). The fission is probably the cause of the 
complexity in the branching and interconnections in all parts of the 
gut m Planaria maculata (pi. 9, fig. 14; pi. 10, figs. 20, 22, 23; pi. 
11, fig. 31). Many other planarians have long branches extending 
from well up on the posterior rami toward the posterior end, while 
anteriorly the gut is quite regular. If fission occurred to any extent 
in these forms it would produce the same kind of irregularity that is 
found in Planaria maculata. Indeed, the production of these 
bizarre connections can often be actually followed, as in plate 9, fig. 
ures 13 and 14. Zacharias (’86) was struck by the great complexity 
of the gut branching in Planaria subtentaculata., but did not corre¬ 
late it with the fission in that species. 
In many cases the tail pieces redivided before the pharynx had 
reached its normal position or the proportions of the adult had been 
attained (pi. 10, figs. 20, 21). The only requisites for a new division 
