142 BULLETIN OF THE 



they are found on the partitions immediately below the colony-wall. 

 Still later (Plate VI. Fig. 59, mu. rot., mu. ret.) we see them on the lower 

 portion of the partition, and finally (Fig. 56, mu. rot., mu. ret.) they are 

 found attached to the sole, at some distance, it may be, from the 

 radial partition. 



The question arises at once, How do these changes of position take 

 place 1 Examination shows that the union between the coelomic epi- 

 thelium and the cells of that portion of the funiculus which is attached 

 to the roof is very slight after the funiculus has passed to some distance 

 from the mother polypide. Although occasionally I have seen the cells 

 of the fixed end closely applied to the coelomic epithelium, the only 

 connection between the two is usually effected by means of amoeboid 

 cells (Plate V. Figs. 46-48, cl. mi.). On cross sections of the fixed end 

 of the funiculus these cells (Fig. 49, cl. mi.) are seen to surround it as 

 a loose layer, and in longitudinal sections some of the amoeboid cells 

 are seen to be connected with the coelomic epithelium. It is difficult to 

 determine the origin of these cells, but they have the position and 

 character of the cells of which the funiculus was exclusively composed 

 before the entrance into it of the ectodermal plug described by Braem. 

 The only explanation of the migration of the funiculus which occurs to 

 me has been suggested by the facts given above ; namely, that the 

 " migratory cells,'' by which the funiculus is attached to the coelomic 

 epithelium, change their position, carrying with them the funiculus. 

 Remembering that the coenocoel is filled with a fluid in which the 

 funiculus floats, and that by the growth of the funiculus it is elongated 

 in proportion as the distance from its origin to the ccecum increases, this 

 hypothesis does not seem improbable, although its truth can hardly be 

 tested by the study of preserved material. When the funiculus has 

 reached its permanent position its attachment to the coelomic epithe- 

 lium is more intimate. Meanwhile the end attached to the polypide 

 has become more and more attenuated (Plate IX. Fig. 77, fun.), until, 

 in the adult, I have usually been unable to discover any attachment. 

 In any case, it must certainly be broken when the polypide begins 

 to degenerate. 



The migration downward of the ends of the muscles which are 

 attached to the partition is even more difficult of explanation. During 

 this migration their point of origin seems to be in the muscularis of the 

 partition itself. The fixed point of the muscle in the adult is probably 

 in the muscularis of the sole, since I have traced muscle fibres through 

 the coelomic epithelium, and to the muscularis (Plate VI. Fig. 58, mu. 



