30 AUX. 17. — N. YATSU. 



C, 1) — note ail are the larvie of C. marginaius). Excepting 

 these abnormal cases the pilidia Averc affected very slightly. 

 This series taken with the previous one (Series U) may show 

 that the disarrangement of the organ bases due to abnormal 

 cleavage is restored in some way or other during the course of 

 development, so that in the end the resulting larvas may assume 

 a form deviating not very much from the ordinary one. Yet 

 that the regulation is not altogether complete is shown by the 

 fact that sometimes multiple apical organs are produced. A 

 case similar to this may be found in the ^-hirva of Cynthia, in 

 which the sense spots formed are abnormally numerous (Conklin 

 '05 p. 169). 



Series W. Embryos reared in Ca-free Sea-water. 



The eggs were shaken so as to remove their membrane and 

 were kept over night in Ca-free sea-water. These eggs yielded 

 cell-masses with hardl}'- any differentiation at all. One notices, 

 however, in some of them the apical flagellum and ciliated patches 

 (Fig. 26 A-D). It should here be mentioned that on examina- 

 tion with a high power loose cells were found mixed with the 

 above cell masses, and these cells had cilia not in a restricted area 

 but scattered over the surface (Fig. 26 F, G). It is, I think, 

 hardly necessary to add that this peculiar arrangement of cilia 

 upon the cell is due to abnormally disposed centrioles in the 

 cytoplasm. The position of the centrioles, it may be deduced, is 

 in this case not predetermined in the cell to be ciliated, but is 

 secondarily fixed by the mutual relation of adjacent cells. 



When such poorly differentiated embryos are put back into 

 ordinary sea-water, they change their entire aspect, the external 



