26 BULLETIN; MUSEUM OF COMPARATIVE ZOOLOGY. 



largest in the early spring immediately before the eggs are laid, when they 

 often extend the whole length of the genital region and are looped or folded, 

 as are the seminal vesicles ; they are smallest immediately after the egg-laying. 

 A mean between these two extreme conditions is shown in Figure 4. 



The time of egg-laying, as well as of spermatophore formation, depends upon 

 the warming of the water in the spring. One can hasten both processes by 

 bringing the animals for a few days into a heated room. Around Cambridge 

 the eggs are laid mostly in the months of April and May. Small-sized indi- 

 viduals, however, may come to maturity later in the season, even as late as 

 September. 



The eggs are pink in color and about 0.3 mm. in diameter. They are 

 attached to the under surface of the body in groups of two to eight eggs each. 

 Each group is enclosed in a separate, delicate, transparent sac, which adheres 

 to the under surface of the body. The sacs are arranged in two longitudinal 

 rows close together, one on either side of the median plane of the body. The 

 more posteriorly placed sacs usually contain more eggs than those farther 

 forward. 



I have not observed the process of egg-laying, but believe that the eggs of a 

 single sac are laid at about the same time, that they are then crowded back as 

 far as possible under the body, and that there is poured over them a secretion 

 from the clitellar glands which hardens into the delicate wall of the sac. After 

 a period of rest, during which the body is closely applied to the group of eggs 

 so that its sac becomes fastened to the body, another group of eggs is laid, and 

 so on until all the mature eggs have been expelled from the ovary. The cli- 

 tellar glands are deep-seated, unicellular epidermal glands opening on the 

 ventral surface in the vicinity of the female genital pore. They can be 

 demonstrated by niethylen-blue staining. 



Animals which are kept in aquaria lay their eggs at night, and always com- 

 plete the process in a single night, so that all the eggs borne by an individual 

 are in about the same stage of development at one time. 



I think it probable that the egg sacs are arranged in the order laid, from 

 behind forward, for in one of the most anterior sacs a single egg is occa.«ionally 

 found, but never in one of the more posterior sacs have I observed so small a 

 number. The number of eggs laid by an individual depends upon its size. 

 An animal thirteen mm. long (when fully extended) was found to have laid 

 sixteen eggs ; another twenty-six mm. long was found carrying forty-five eggs. 

 The average number for nine individuals examined at one time was thirty-one. 



The usual number of egg sacs formed is six or eight ; in one case examined 

 it was ten. The average number of eggs found in a sac is about four ; for the 

 most anterior pair of sacs it is three. 



e. Digestive Tract. 



The position of the mouth {or, Figures 3, 7), except when tlie body is much 

 contracted, is anterior to the eyes, in the third somite (ring 2). 



It leads dorsally into the pharyngeal sac (sac. phy., Figun- 7), wliicli con- 



