18 SIDNEY V. HABMEE. 



much the same as in the former figure. The tentacle-sheath 

 is, however, now becoming less definite. To the left of the 

 figure it is hardly distinguishable from the follicle, with which 

 it probably fuses. 



The embryo is practically unaltered, except that it has come 

 to the surface of the follicle ; but the principal difference 

 between this and the earlier stage concerns the follicle itself. 

 This structure no longer forms a compact mass of granular, 

 nucleated protoplasm, as in fig. 6 ; but it has become distinctly 

 vacuolated. This vacuolation is the beginning of the process 

 by which the follicle of earlier stages is transformed into the 

 protoplasmic reticulum of later stages. 



Fig. 9 (PI. II) well illustrates the manner in which this 

 transformation is effected. The tentacle- sheath is not so clear 

 as in the former stage, and can, indeed, hardly be distinguished 

 except at its upper end. "Whilst in earlier stages it filled up 

 most of the ovicell, it has now collapsed to a large extent. 



The proximal portion of the follicle is in this ovicell still 

 solid, and is perfectly similar in structure to the solid follicle 

 of fig. 6. Distally the follicle is almost unrecognisable, having 

 become separated by enormous vacuoles into strands of anas- 

 tomosing, nucleated protoplasm. These strands are, however, 

 most unmistakably continuous with the proximal, solid portion 

 of the follicle. The embryo is practically unaltered, still 

 forming a small rounded mass of undifferentiated embryonic 

 tissue lying in a part of the reticulum. 



The great increase in the size of the follicle and in the 

 number of its nuclei up to the stage shown in fig. 11 is pro- 

 bably connected with the development of a nutritive arrange- 

 ment for the young larvae. The minute egg-cell of fig. 1 gives 

 rise, as I believe, to the embryogenic organ of fig. 11, and this 

 to the numerous young larvae with which the mature ovicell is 

 crowded. These larvae lie in the meshes of the protoplasmic 

 reticulum, from which they are probably supplied with nutri- 

 tive material. 



In figs. 6 and 9 the base of the ovicell has a very characteristic 

 structure, always noticed in young ovicells at certain stages. 



