CASTLE: NORTH AMERICAN RHYNCIIOBDELLIDiE. 25 



lateral limits of the median lacunar space. This space the vas deferens enters in 

 company with the ducts of the salivary f^lands, 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 them, being capable apparently of 

 great enlargement. Sometimes the vesicle runs back as far as the pair of long 

 crop diverticula in somite xix. (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- 

 wanl again and, narro\ving, continues as the muscular and glandular ejaculatory 

 duct (Figure 4, dt..ej.). 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. $, 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 (" Clepsine 

 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 



