236 PROF. W. A. HASWKLL : 



In young females of Grubea kerguelensis there are four small ova on each 

 side in each segment. Two of these occupy a position in the segment 

 corresponding to that occupied at first by the only two in Exogone fustifera, 

 lyino- nearly transversely — the other two are situated laterally. Each of the 

 transverse ova is situated in a thin- walled sac (nephridium) opening in the 

 usual position, and there can be little doubt that the investment of each of 

 the other ova is a prolongation of this sac. 



So far as the material at command goes, Grubea quadrioculata corresponds 

 closely in the female reproductive apparatus to G. kerguelensis. 



Embryology. 

 For our earliest information on the development of the Ewogonea? we are 

 indebted to (Ersted (25), who gave a brief account of some of the stages as 

 seen in his Exogone naudina. 



Viguier (34) notes some points in the development of Exogone gemmifera. 

 The segmentation stages figured do not, the author acknowledges, throw any 

 light on the mode of formal ion of the germinal layers, but he thinks it 

 probable that there is an invagination the orifice of which becomes the anus. 

 The buccal invagination appears somewhat late. When the larva becomes 

 detached it possesses five setigerous segments. 



De Saint Joseph (31) describes various stages in the later development of 

 E. clavigera and makes an interesting observation on the difference between' 

 the development of Grubea clavata and G. pusilla which will be referred to 

 later. 



The only other recorded observations on the embryology of the Exogonece 

 are those of Pierantoni (28). This author made a noteworthy contribution 

 to our knowledge of the remarkable phenomenon of epigamy ; but the 

 objects which he aimed at in his research did not include a complete stud)' 

 of the embryology. His results as regards the embryology of Sphcerosyllis 

 hystrix may be summarised as follows : — 



The ovum divides into two blastomeres of which one divides rapidly into 

 two, four, and eight, while the other divides much more slowly. From the 

 successive divisions of the former blastomere there result a great number of 

 micromeres (ectoderm) and from those of the other a very small number of 

 macromeres (endoderm) which ultimately become enclosed within the micro- 

 meres ; the former at this stage are only eight in number. 



Both miuromeres and macromeres increase in number, but, as regards the 

 latter, after the s age of eight cells it is no longer possible to distinguish the 

 individual elements, the whole appearing as a mass of red yolk-matter. 



In Exogone fustifera the ova when discharged are fixed to the ventral 

 surface just internal to the ventral cirri — the attachment being effected, as 

 already stated, by means of the secretion of the ventral pedal glands. A 

 pair is attached to each segment from the 11th or 12th as far back sometimes 

 as the 43rd or 44th. 



