Phystology 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 
m a direction reverse to the first, and soon. [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 immoyeable, 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 phenomenon 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 im the ‘ Archives’ of Miiller for 1835, p. 586), and recently, 
in speaking of the same phenomenon 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 cilia. 
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 
m 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 lmes below the first 
pair of fins, contain, at the side of the ova, a considerable quan- 
tity of seminal fluid, the spermatozoa of which exhibit very lively 
movements, as is indeed the case with those of other animals at 
the rutting period. 
The question still remaims to be ascertained, whether the Sa- 
gitte fecundate mutually, or whether they are androgynous. With 
respect to this poimt, I must attribute great weight to a constant 
phenomenon 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 
