Physiology of Sagitta bipunctata. 297 
‘the seminal fluid is elaborated. The Sagitta therefore presents 
no seminal gland organized in the manner of a testicle. 
The apparatus destined to contain and to convey the mature 
seminal fluid is very singular. It is already known that each cell 
opens exteriorly, before the caudal fin, by an aperture situated on 
a rounded promimence. This prominence is excavated and com- 
municates with a canal hollowed in the thickness of the skin of 
the tail, and which goes finally into the cell of the corresponding 
side. In fact, if we open each cell inferiorly, by a longitudinal 
section, and examine the interior surface of the upper wall thus 
exposed, after havimg removed with the greatest care all the vis- 
cous matter, we distinctly observe, with a magnifying power of 
ten to twelve diameters, that at a small distance from each pro- 
minence there is a rounded aperture with swelled margins. This 
cavity leads into the canal above-mentioned, which extends pos- 
teriorly, followmg the margin of the upper muscular band, and 
describing a slight curve. At first somewhat broad, it gradually 
becomes more and more narrow, and opens into the cavity of the 
prominence. ‘This cavity is relatively very large, and appears, 
for this reason, to serve to collect and preserve the seminal fluid, 
before its final exit. The internal sides of the two excretory ca- 
nals, and the apertures with swelled sacculated margins are 
covered with a fine membrane furnished with very numerous long 
cilia close together and very vibratory. 
Seminal fluid—The mature fluid is of a chalky-white colour, 
thick, and formed solely of spermatozoids. It is often found on 
the external aperture of the seminal cells in the form of flakes or 
drops. When one of these drops is observed with the microscope, 
the phenomenon known by the name of total movement of the 
seminal mass is instantly observed. The spermatozoa are capil- 
liform, much elongated, and evidently narrowed toward their two 
extremities, where they are pointed; they have an undulatory 
or serpentine movement. 
The results of my researches on the development of these bo- 
dies are very limited ; I believe however that they agree generally 
with those of Dr. Koelhiker on certain Annelides, and in parti- 
cular on the Branchiobdella parasita or Pontobdella spinosa. {See 
his memoir entitled “ Beitrage zur Kenntniss der Geschlechts- 
verhaltnisse und der Samen-flussigkeit wirbellosen Thiere,” pp. 18 
and 24.| In all the individuals except those in which the period 
of fecundation is near, and even in those which are only two lines 
and a half long, bodies resulting from the agglomeration of a 
great number of vesicles, or of small and spherical cells, are per- 
ceived in the limpid seminal fluid ; these are the bodies known by 
the name of aggregations of cells (Zellenhaufen), or by the still 
more recent name of seminal globules (Samenkugeln) : it isin these 
