544 PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
directly or through intervening testes with the vas deferens of its 
side. In species with a smaller number of testes it is not difficult 
to discover the connection of each testis with the vas deferens. In 
Planaria maculata, the testes communicate with one another or 
with the vas deferens in the same way and it is only their great 
number which makes the exact connection impossible to establish in 
manv cases. 
During the egg laying season the vasa deferentia (pi. 12, figs. 83, 
34, vd) may be found as very fine tubes extending from the most 
anterior testes and everywhere receiving testicular canals. Their 
diameter increases in the region of the pharynx where, swollen with 
spermatozoa, they become the seminal vesicles as in other Planaria. 
In the live worm, they may be seen through the ventral surface as 
two whitish masses on either side in the region of the pharynx. 
Posteriori}^ the seminal vesicles narrow suddenly and the smaller 
tubes thus formed turn with a shai-p angle, mount dorsally, and then 
turn ventrally to the base of the penis where each opens into an 
enlargement {en) of the penis lumen. This lumen is of considera¬ 
ble size and has a blind anterior end, but is drawn out posteriorly 
into a liner tube and opens by a small aperture on the free end of 
the penis (jy). The penis (pi. 12, figs. 33, 34, is short and thick, 
closely invested by the walls of its cavity and pointing downward 
and backward at an angle of about 45°. Along its median poste¬ 
rior face it joins the atrium by a thin mesentery-like fold so that a 
sagittal section (pi. 12, fig. 34) shows as though there were only 
a shallow furrow around the penis posteriorly. The outline of such 
a sagittal section is given in figure 34 and the depth of the atrium 
immediately on either side of this "is indicated by a dotted line. 
Behind this anterior part which contains the penis, the atrium is 
narrowed abruptly. It is worth noting that the longitudinal axis of 
the penis does not point in the direction of this opening (pi. 12, fig. 
34), but downward and backward as above described and thus the 
free end of the penis lies somewhat below the opening through 
which it must pass when protruded. The contraction of muscle 
fibers in the mesentery-like fold may perhaps aid in guiding the 
jDenis out posteiiorly. The narrow portion of the atrium soon 
widens abruptly by sending a larger branch ventrally and slightly 
backward to communicate with the outside at the genital pore [gp). 
At the upper posterior angle of the main atrial cavity the vagina 
