Further Studies on Reproduction in Sagitta. 301 



segmenting eggs of other hermaphrodite organisms, and in either 

 male or female germ cells of those insects in which an equal pair 

 of heterochromosomes has been described in the male germ cells. 



It is my intention to investigate further some of the points re- 

 ferred to in this paper as soon as there is opportunity to work 

 again on fresh material. 



I desire in this place to express my appreciation of the oppor- 

 tunity afforded me to collect material at Pt. Erin, Helgoland and 

 Naples, and of the privileges and courtesies which I enjoyed at 

 the Zoologisches Institut, Wiirzburg, and. at the Stazione Zool- 

 ogica, Naples. 



Summary 



1. Eggs of Sagitta, when ripe, apparently make their way into 

 a previously closed oviduct and move down the oviduct to the 

 reproductive pore by their own activity. 



2. The ovary proper and the ducts are entirely distinct struc- 

 tures as to their origin. Each ovary develops from one of the 

 four primary germ cells, while the antrum and oviduct develop 

 from a fold or outgrowth of the mesodermal layer of the body wall 

 below the ovary, and the cells which form the sperm-duct or ' sper- 

 mentasche ' originate from the oviduct wall by migration or de- 

 lamination. 



3. It is suggested that the deeply stained network that can 

 often be seen in the median part of the oviduct wall next to the 

 sperm-duct may be of an elastic nature. 



4. In Sagitta elegans eggs free in the ovary have been found in 

 all stages between that of the metaphase of the first maturation 

 mitosis and a 16-cell stage. No satisfactory explanation of this 

 phenomena was apparent. 



5. Elpatiewsky's 'besondere Korper' was found in all of these 

 free eggs, beginning with the stage in which the two pronuclei 

 were in the center of the egg. 



