POLYCILETA OF THE L.M.B.C. DISTRICT. 249 



Arenicola castings, while wherever I found the smaller 

 the worm Scolopos armiger was sure to be piesent. Both 

 kinds of egg-cocoons were anchored in the sand by a 

 gelatinous cylindrical stalk descending some two or three 

 inches into the sand. In the case of the green cocoons 

 the stalk soon became ragged and shredded ; in the brown, 

 it continued perfectly cylindrical and entire for most of the 

 distance traced. 



I. Development of Scolojrfos : — The small brown cocoons 

 certainly appertain to this animal, for besides the fact that 

 this worm is always found close to the egg masses — 

 animals examined February 21st contained ova identical 

 with those least developed in the cocoons. The size of 

 the cocoons differed somewhat ; the largest being 2 cm. 

 by 1 cm., stalk 10 cm. at least. The later stages of 

 development are well figured by Cunningham and Ramage 

 and also by Schultze, and I have nothing to add to their 

 descriptions. As to the progress of segmentation, hither- 

 to undescribed, the following is a summary of what I have 

 observed : — The ova are 0"25 mm. in diameter. Each 

 shows a very distinct germinal vesicle. Two polar bodies 

 are excluded and following quickly is the division of the 

 vitellus into macromere and micromere (PI. XIV, fig. 3). 

 The latter very rapidly sub-divides into very small cells 

 which gradually overspread the few large cells derived 

 from the primitive macromere, until finally only a small 

 opening — the blastopore — is left in the enveloping layer 

 of micromeres. Usually the number of derived macromeres 

 is either two or four at the stage of enclosure by the 

 micromeres. These latter are, I believe, not all derived 

 from the primitive micromere, being added to from time 

 to time by small cells fissioned off from certain of the 

 macromeres. (Salensky observed a similar process during 

 his elaborate investigation of the embryology of Nereis 



