RELATIONS OF SAGITTA BI PUNCTATA. 23 



contents.* These will be seen constantly ascending on the 

 outer, and descending on the internal wall or septum in the 

 directions indicated by the arrows in fig. 4. The cause of this 

 motion is stated by Krohn to depend upon the presence of 

 scattered cilia in the posterior part of the cavity. 



The spermatozoids thus formed make their exit from the 

 cavity in a very curious mode. On each side of the caudal 

 portion will be observed a projection, (figs. 1 and 4, e e,) which 

 may, perhaps, be regarded as a sort of ejaculatory apparatus. 

 These processes are hollow sacculi, which open externally by a 

 rounded orifice situated at the upper end, and communicate 

 with the interior of the compartment to which they belong, 

 through a canal excavated in the integuments of the caudal 

 portion. If, as Krohn observes, one of the seminal compart- 

 ments be laid open by a longitudinal incision on the under 

 surface, and the contents carefully removed, an opening sur- 

 rounded by a raised margin will be clearly seen at a short dis- 

 tance from each ejaculatory sac. This orifice leads into the 

 canal above mentioned, which runs along the corresponding 

 border of the upper muscular band, making a slight curve 

 posteriorly, gradually contracting in size, and finally opening in 

 the cavity of the ejaculatory sac. The inner wall of these 

 efferent canals, as well as of the external sac, is lined with an 

 actively vibrating ciliated membrane. 



With respect to the mode in which the spermatozoids come in 

 contact with the ova nothing is known, though it would seem, 

 if Krohn's observation above related, of the presence of sper- 

 matozo ain the caecal canal contained in the ovary be confirmed, 

 that they must make their entrance in some way into that 

 organ. It is more probable, however, that the ova are impreg- 

 nated after extrusion ; and that this is the case, is rendered 

 the more likely by the circumstance that innumerable sperma- 

 tozoids in the most active motion may occasionally be observed, 

 swarming out of the orifice of what I have termed the ejacula- 

 tory sac (fig. 5). And it seems scarcely possible that these 

 motile filaments should make their way spontaneously into the 

 narrow and close opening of the oviduct, which they must do 

 in order to reach the canal in question. 



The Sacjitta is obviously oviparous ; but with respect to the 

 further development of the ova after deposition, little is known. 

 According to Krohn (Wiegm. Arch. 1853, p. 270), the vitellus 

 consists of numerous cells containing an albuminous fluid, and 

 in which he was unable to perceive any vitelline granules. 

 It is surrounded by two membranes. The internal, which 



* Krohn remarks (p. 13), that a similar movement of tLe spermatic 

 globules is observed in the testicular vesicles of the Leech. 



