166 W. B. BENHAM. 



two portions of the funnel, and that opening into the 13th 

 somite {ov. f.) is very small ; in the second section beyond 

 this it is absent. But that part of the funnel communicating" 

 with the ovisac (ov, /.) is of much greater extent, and occupies 

 a large part of the outer wall of the ovisac. It is still present 

 in fig. 27, five sections further on, where it lies on the dorsal 

 wall of the ovisac, and does not cease till two sections beyond 

 this, so that it passes through about six more sections than 

 does that part which communicates with Somite xiii. Each 

 section is '1 mm. thick, so that the size of this funnel is 

 about 1 mm. in extent, of which only about '5 mm. com- 

 municates with Somite xiii. 



There is thus an approach to the condition met with in 

 Eudrilidse, where the funnel opens entirely into the ovisac. 



The ovisac itself is thin-walled and slightly subdivided; 

 in the sac of one side were two ova (fig. 28 represents a portion 

 of the fourth section of the series after fig. 27). Each of these 

 exhibits karyokinesis (see fig. 29, which is drawn from the 

 next following section), in which the spindle with the chromo- 

 somes arranged at the equator and the '' centrosome" and 

 polar rays at its poles are very well seen. The one sketched 

 was sectionised along the axis of the spindle; the other ovum, 

 lying at its side, was cut at right angles to the axis. 



Each of these ova measures "3 mm. — exactly the same 

 diameter as the largest ovum in the ovary ; it is surrounded by 

 a thick " vitelline membrane," which in the one sketched was 

 folded at two points, owing, no doubt, to contraction. 



These two ova appear to be undergoing changes preliminary 

 to the formation of polar bodies. 



I am not aware whether this phenomenon has hitherto been 

 definitely recorded as occurring in the ovisac;^ but there is 

 little doubt that such is the case, the ova undergoing matura- 

 tion here just as the spermatozoa attain their complete con- 

 dition in the sperm-sacs. 



1 Vejdovsky, in liis " Entwickelungsgeschichte," finds that the polar bodies 

 in B,hyuchelmis are formed iu the ovisac, while iu Lunibricus and 

 Allolobophora they are not formed till the ova are laid iu the coeoou. 



