V< "' :| | Robertson. — Embryonic Fission in Crisia. L39 



septum,* (chi. r.) probablj serves as a supporting structure to 

 keep the embryo from passing downward into the narrow portion 

 of the ovieell, but the whole tube .seems to be related to the great 

 development of the second follicle in this species. In ('. eburnea 

 the follicle of the adult ovieell consists of a relatively small num- 

 ber of cells scattered among its contents (PI. XV, Pig. 28). In 

 ('. occidentalis, however, the second follicle is a mass of cells in 

 which the embryos and larvae are imbedded (PI. XV, Fig. 29). 

 With the disappearance of the spherical follicle and the appear- 

 ance of a second follicle, the embryo attains a relatively enormous 

 size before budding begins. 



The Secondary Embryos.— An early budding stage is shown 

 in PI. XIV, Fig. 27. This is drawn to the same scale as Figs. 25 

 and 2G, and a comparison with these two figures will give an idea 

 of the great size which the embryo attains, this one being 200 fi. 

 m its longest diameter. As the embryo increases iu size it comes 

 to occupy a higher position in the ovieell, moving upward appar- 

 ently to the point where the walls are more widely expanded. 

 This is especially noticeable in Crisia mnoilit where the ovieell 

 is widest at the distal end. The embryo is not anchored in any 

 way in G. eburnea, and is often found at the top of the ovieell 

 close against the valvular closure (PI. XV, Fig. 28, prim, ebm.) 

 Buds are formed at various places on the body of the embryo. In 

 the casi- represented in Fig. 27, two somewhat irregular processes 

 project distally, from the extremities of which small portions are 

 constricted (sir. emb.) . These are not the only budding regions, 

 however, for on other parts of the surface outgrowths occur 

 which as other sections reveal, are incipient buds (in. bd.) At 

 the proximal extremity there are a few cells which the examina- 

 tion of preceding sections shows belong to another bud (sec. emb.) . 

 There are instances also where the first buds are constricted from 

 the extremities of lone' arms extending proximally through the 

 whole length of the ovieell. The primary embryo frequently 

 possesses a somewhat rounded triangular form, and the buds are 



•The septum found in rh<- base of the ovieell of 0. identalis is probably 



homologous with the chitinous articulation occurring on each zocecium of this and 

 the related species, C. geniculata and O.cornuta. Evidence for this homology will be 

 given in a later paper. 



