288 ^ N. M. Stevens. 



the oviduct wall stain as though they contained supporting fibers 

 or possibly muscle fibers, though in watching the passage of eggs 

 down the oviduct I have been unable to detect any muscular 

 activity in the oviduct walls. I have thought that these fibers 

 might be of an elastic nature, but have not tested their staining 

 reaction with this point in view. They stain deeply with iron- 

 hsematoxylin, but so does any particularly dense portion of a cell. 

 The stretching to which the walls of the oviduct are subjected 

 when eggs are passing through it naturally suggests that the cells 

 may have developed material of an elastic or supporting nature 

 to meet this strain. 



Maturation and Segmentation of Eggs in the Ovary 



While making the above observations on egg-laying in Sagitta 

 elegans, it was noticed that in several individuals asters were 

 present in eggs which were either free in the ovary or were in the 

 oviduct. The first cases noted were in material which had been 

 kept in the laboratory over night, but later the same phenomenon 

 was observed in individuals fresh from, the sea. Several such speci- 

 mens were fixed and sectioned. Eggs were found free in the ovary 

 in all stages of maturation and segmentation up to an 8-16-cell 

 stage. Fig. 23 shows the first polar body and the second polar 

 spindle of such an egg, and Fig. 24 the uniting male and female 

 pronuclei. Figs. 25 and 26 are the first and second segmentation 

 spindles in metakinesis and anaphase respectively. These figures 

 make it plain that development here is that of fertilized eggs and 

 not a case of parthenogenesis. Fig. 27 is a section of an 8-cell 

 stage from an ovary in which several segmenting eggs were found. 

 At present I have no satisfactory explanation to offer for this 

 premature development of Sagitta eggs. Nothing of the kind was 

 seen, either in material from Naples or in that from Woods Hole 

 in 1904, the only approach to it being the cases of two polar 

 spindles in eggs of one individual described in "Further Studies 

 on the Ovogenesis of Sagitta" ('05, p. 246, Figs. 11, 15, 16, and 

 17). Whether these segmenting eggs could ever be laid seems 

 doubtful, for the moment of breaking away from the oviduct 



