Further Studies on Reproduction in Sagitta. 287 



The sperm-duct tissue has not appeared in the antrum region. 

 By comparing this figure with Fig. F, one can easily see the rela- 

 tion of the embryonic layers to the adult oviduct and sperm- 

 duct. In one case only, shown in Fig. 16, have I ever seen at this 

 stage the sperm-duct tissue separated from the median oviduct 

 wall, leaving a lumen corresponding to the space through which 

 the ripe eggs pass to the exterior. 



Somewhat later the whole oviduct with the eontained sperm- 

 duct tissue contracts laterally, as shown in Fig. 17, changing the 

 flat layer of sperm-duct tissue into an approximately cylindrical 

 rod of syncitial tissue with nuclei rather irregularly scattered and 

 vacuoles here and there (v). Figs. 18 and 19 show the appearance 

 of an irregular lumen, and Fig. 20 the presence of spermatozoa 

 in the more regular lumen of an older duct. In Fig. 21 we have a 

 longitudinal, but slightly oblique, section through the reproduc- 

 tive opening and antrum of an adult Sagitta, showing the relation 

 of the two ducts and their openings when the sperm-duct is slightly 

 open and the oviduct closed. In Fig. 22 is shown a transverse 

 section of an ovary of Sagitta bipunctata with a ripe egg in the 

 oviduct, to the outer wall of which the sperm-duct (sd) remains 

 attached. The walls of the oviduct are much stretched, but the 

 lateral wings are not opened as one might expect them to be. 



Thus we have traced the development of the oviduct from its 

 origin in a fold of mesoderm at the base of the ovary, and the for- 

 mation within it of a sperm-duct or ' Samentasche ' with a separate 

 opening from that of the oviduct. These ducts are without 

 doubt purely accessory mesodermal structures, and have no 

 direct connection with the germ track of Sagitta. In adult 

 ovaries the young oogonia and youngest oocytes are sometimes 

 crowded against the median wall of the oviduct, and are even 

 pressed in between the cells in such a manner that they appear 

 to be a part of it, but I am convinced that this is only a secondary 

 appearance and that there is always a portion of the oviduct wall 

 between the germ cells and the sperm-duct. 



The oviduct wall furnishes two accessory fertilization cells to 

 each ovum, and the lateral wings m.ay be largely reserve cells to 

 make good the loss from this source. The central ends of the cells of 



