CASTLE: NORTH AMERICAN RHYNCHOBDELLIDA. 25 
lateral limits of the median lacunar space. This space the vas deferens enters in 
company with the ducts of the salivary glands, which here pass inward to join 
the base of the proboscis (Figure 1, gl. sal.) Having reached the median lacuna, 
the vas deferens turns backward, running usually ventral and lateral to the diges- 
tive tube and parallel with the course of its collecting portion. In the median 
lacuna it winds about more or less, or may even cross into the opposite half of 
the body as a result of its being crowded for room either because of its own dis- 
tended condition or from the condition of other organs in its vicinity. As it runs 
backward it widens into a spacious seminal vesicle (Figure 4, vs. sem.), and its 
epithelial lining ceases to be ciliated. The dimensions of the seminal vesicles 
vary with the amount of sperm stored in then being capable apparently of 
great enlargement. Sometimes the vesicle runs back as far as the pair of long 
crop diverticula in somite x1x. (Figure 1), and is crowded out in the form of 
one or more loops between the testes (Figure 4); it may even find room for 
itself by crossing into the opposite half of the body. Ultimately it bends for- 
ward again and, narrowing, continues as the muscular and glandular ejaculatory 
duct (Figure 4, dt. ej7.). The ejaculatory duct, as it runs forward, passes out- 
side of the inner row of dorso-ventral muscles at about the point where the 
collecting portion of the vas deferens enters the median lacuna. It then runs 
forward into somite xI., where, turning sharply back again, it expands into 
a thick-walled “terminal horn,” which, uniting with the terminal horn of 
the other half of the body, opens to the outside by the mid-ventral male genital 
pore (po. g, Figure 4). The special function of the ejaculatory duct and par- 
ticularly of its terminal horn, Whitman (’91) has shown to be the formation 
and extrusion of the spermatophore. 
In the early spring, as the water in the ponds begins to grow warmer, the 
seminal vesicles are seen to be gorged with sperm, and the formation of sper- 
matophores takes place rapidly. These the animals attach to one another’s 
backs. Whitman (’91) has shown that in the case of G. parasitica (‘‘ Clépsine 
plana”) the contents of the spermatophore pass through the integument into 
the body cavity, and that impregnation probably occurs while the egg is still in 
the ovary. A similar process doubtless occurs in the case of G. stagnalis. 
After the period of active spermatophore formation has passed, — it ordinarily 
lasts but a few days or weeks, depending upon the rapidity with which the 
temperature of the water rises, — the vasa deferentia are seen to be greatly re- 
duced in size and the testes quite inconspicuous, though in the fall they were 
the most conspicuous organ in the entire body. 
The ovaries (Figure 4, oa.) are a pair of simple sacs extending back from 
the female genital pore in the median lacuna, usually ventral and lateral to the 
digestive tube. They are attached more or less loosely by mesenterial strands 
of connective tissue to those portions of the vasa deferentia which lie in the 
median lacuna. This connection, however, is so slight that when crowded for 
room an ovary may extend out in loops between the testes, or across into the 
opposite half of the body, just as the vasa deferentia do. The size of the 
ovaries depends upon the state of maturity of the contained ova. They are 
