Physiology of Sagitta bipunctata. 299 



which are frequently effected by a sort of rotation, and resemble 

 a true circulation. In fact, in this latter case, one or several of 

 these bodies progress along one of the sides of the seminal cell, 

 then pass to the opposite side of the same cell, proceed along it 

 in a direction reverse to the first, and so on. [This circulation is 

 far more active and more general in individuals less developed.] 

 In other cases these bodies have very little motion, being some- 

 times attracted and sometimes repulsed by the walls. Frequently 

 indeed the majority of these bodies remain immoveable, until, at 

 a given moment, each begins to move, as if its turn had arrived. 

 Generally these movements do not extend beyond the posterior 

 part of the seminal cells. The cause of this phsenomenon is due 

 to the existence of very minute and at the same time very trans- 

 parent vibratile cilia on the posterior wall of the cells, and which 

 by their motion produce currents in the seminal fluid. 



The seminal globules move also in the same manner in the 

 testicular vesicle of the leech, that is to say, describing a con- 

 tinual circle along the sides of that vesicle. Professor Henle ob- 

 served it several years ago (see his observations on the Branchio- 

 bdella in the ^ Archives ' of Miiller for 1835, p. 586), and recently, 

 in speaking of the same phsenomenon in his beautiful work on 

 the tissues of animals (Allgem. Anatom. p. 211), he states that 

 the cause of it is not well known. But, in all probability, this 

 rotation is equally produced by these vibratory cdia. 



The maturation of the seminal fluid advances in each indivi- 

 dual parallel to that of the eggs, which might be presumed from 

 what has been said on these two products. In a young or 

 in an adult animal, the products of the male and female gene- 

 rative organs are always at an equally advanced period of their 

 development. The result of this is, that at a determined period, 

 the ova and the seminal fluid have acquired a simultaneous ma- 

 turity, and that the fecundating fluid is introduced into the ova- 

 rian pouch. In fact, in certain individuals the fecundation is 

 already effected. Their ovaries, filled with a great number of very 

 large eggs, which extend from two to three lines below the first 

 pair of fins, contain, at the side of the ova, a considerable quan- 

 tity of seminal fluid, the speiunatozoa of which exhibit very lively 

 movements, as is indeed the case with those of other animals at 

 the rutting period. 



The question still remains to be ascertained, whether the Sa- 

 gitt(B fecundate mutually, or whether they are androgynous. With 

 respect to this point, I must attribute great weight to a constant 

 phsenomenon which strikes us when we examine the individuals 

 in question. In fact, the seminal cells in them are constantly 

 empty, without any trace of spermatozoa, which were before so 

 numerous, or at least only a very small number are found, almost 



