THE EGG-CAPSULE. 39 



remarkable venous outlet, and the arterial supply is also highly developed, branches 

 of the oviducal artery passing backward along the oviduct and dividing into an 

 elaborate series of transverse branchlets. * 



The oviduct itself undergoes striking changes to accomplish step by step the 

 stages in the formation of the capsule. To follow these briefly, the oviduct con- 

 tracts cephalad when the egg is received, and holds it in the cavity dilated in the 

 posterior region of the capsular gland. Here it is that the walls of the oviduct 

 form folds and ridges and by these are able to model the secretion of the gland 

 into the beginnings of the capsule. From such a position the early capsule was 

 obtained which is figured in plate in, figure 12. Its shell was papery, whitish (with 

 but a trace of color), and so frail that it could not be removed unbroken with the 

 contained egg. 



The exact mode of folding of the walls of the oviduct to produce the details of 

 the capsule need not be given in detail. The growth in the capsule continues, as 

 shown in plate HI, figs. 13, 14, 15, and 16, the tail-sheath and its appendage of 

 the case being the last portions formed. The fact that the anterior part of the 

 case is finished before the tail-sheath was often taken advantage of by the writer in 

 his effort to secure embryological material, for he found that such an egg as shown 

 in plate n, fig. 8, could be safely incubated for earlier stages if the base of the tail- 

 sheath was kept closed, e. g., by a ligature. 



In comparing the foregoing figures one observes a number of details as to the 

 modeling of the capsule from stage to stage. The earliest condition (plate in, fig. 1 2), 

 shows that the tip of the capsule, although delicate, is almost complete, with 

 opercular folds, serrulae, apex, lateral ridges, and the beginnings of the dorsal 

 keel. In the stage of plate in, fig. 16, the capsule is practically complete, save for 

 the tail-sheath, and in this stage the lateral webs are widest, suggesting the con- 

 ditions of Callorhynchus. 



The oviduct from which such a stage is taken as that shown opened in plate n, 

 fig. 6, forms, as we could naturally expect, an exact mold for the capsule. Thus we 

 find a cervix, c, with sphincter (for apex of the case) ; distinct creases, /. w. (for lateral 

 webs) ; a thickened tract, with folded margins and with median groove, d. k. (for 

 dorsal wall of case, opercular folds, and dorsal keel). As the tail-sheath was not 

 yet developed in this capsule, the corresponding region of the oviduct, /. s., is still 

 contracted ; but at the sides we note the broader folds, r, in which the rugae are 

 laid down ; also at t. o. the deep recesses below the capsular gland in which the 

 terminal organ comes to be formed. At a subsequent stage the lateral webs are 

 strengthened by a process of folding, which causes them to become narrower (cf. 

 plate 11, fig. 10, and plate in, fig. 16) ; and at the same time the tail-sheath is laid 

 down (plate i, fig. i). 



In the latter process the sheath itself, with the beginnings of its caudal pores, 

 is formed before the adjacent web (plate 11, fig. 7), and when this is completed there 

 remains to be formed only the capsular filament and adhesive organ. By this time, 

 however, the capsule has acquired such a phenomenal length that it extends from 

 the oviducal (i. c. retroanal) opening forward to the anterior wall of the body-cavity 



* The oviducal artery divides into four branches when it reaches the anterior end of the capsular gland, two beccm- 

 ing dorsal, two ventral, and thus they proceed, bilaterally arranged, as far as the posterior portion of the oviduct (</. 

 plate i, fig. i; plate n. figs. 5 and 7). 



