78 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



with that of the oviduct (Fig. 10, ov'dt.), Figure 11 is taken from 

 another zooid and shows the opening of the peribranchial portion of 

 the stalk into the right peribranchial sac. As the pouch is completely 

 separated from its zooid long before the larvae are mature, the only 

 function of this peribranchial orifice is to serve as a passage for the 

 spermatozoa. The vas deferens (va.df.), which is closely applied to 

 the deep wall of th^ oviduct until the latter joins the oviducal part of 

 the pouch, extends much farther forward and opens into the cloaca near 

 the anus. It is thus seen that the oviducal portion of the pouch is a 

 continuation of the oviduct into the pouch, and that the egg never 

 reaches the peribranchial sac at all, but is conveyed directly to the 

 bottom of the poucti. 



The lumen of the oviducal part of the pouch is even narrower than 

 that of the oviduct, so that here too the egg is greatly elongated in 

 its passage. Figure 18 (Plate 3) shows an egg the greater part of 

 which has just entered the pouch; but a small portion of it has not 

 quite emerged from the oviducal tube, and can be seen as a small pro- 

 jection from the rest of the ovum. From the fact that there are no 

 muscles present in the pouch, and none but the heart muscles in the 

 abdomen, and because the ovum has shrunken away from the walls of 

 its conducting tube in preserved specimens, I believe that this com- 

 pression is not due to the killing reagent, but represents a normal 

 condition. 



I have not been able to discover the pouch at the very beginning of 

 its development, and so cannot say whether it is formed as an evagina- 

 tion from the peribranchial sac, from the oviduct, or from both. It is 

 probable, however, that even if the first stages were found it would be 

 difficult to settle this matter, so that a comparative anatomical investi- 

 gation of the subject in Colella, for instance, where all grades of pouch 

 formation obtain, would be more profitable. I have, however, found 

 the fundament when it was only a short cylindrical outgrowth about 

 150 n long. At this stage it presents all the essential features of the 

 adult except that the pouch proper is very little enlarged. In fact 

 Figures 9 to 11 (Plate 2) were taken from a stage but little older 

 than this. Zooids with pouches in this condition are about 2 mm. 

 long, that is about two-thirds grown. The vas deferens, however, is 

 filled with spermatozoa apparently ready to be discharged. Subsequent 

 development consists in a swelling of the pouch, and an elongation of 

 its stalk, so that the whole structure moves posteriorly into the colony at 

 some little distance from the zooid producing it. When the bottom of 



