Physiology o/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 prominence. 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 having removed with the greatest care all the vis- 

 cous matter, we distinctly observe, with a magnifying powder 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, following 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 phsenomenon 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. Koelliker on certain Annelides, and in parti- 

 cular on the Branchiobdella parasita or Pontobdella spinosa. [See 

 his memoir entitled " Beitriige zur Kenntniss der Geschlechts- 

 verhaltnisse und der Samen-flussigkeit wirbellosenThiere," 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 {Zellmhaufen), or by the still 

 more recent name of seminal globules (Samenkugeln) : it is in these 



