BANCROFT: OVOGENESIS IN DISTAPLIA OCCIDENTALIS. 77 



Distaplia t^^pe. Caiman ('94, p. 10), however, in describing the 

 genus Julinia, which is closely related to Distaplia, gives a description 

 of a spherical vesicle attached to the dorsal side of the thorax which 

 he believes to be an incubatory pouch, though no eggs or embryos were 

 found in it. The most significant thing about his account is that the 

 lumen of the oviduct seems to be continuous with that of the pouch. 



2. Observations. 



The incubatory pouch in Distaplia occidentalis is not so large as in 

 some other members of the genus. It usually contains two embryos, 

 and never more than three, according to my experience, while in D. 

 magnilarva, according to Delle Valle's figure ('82, Fig. 5), the pouch 

 may contain as many as eight. The conditions vary in different 

 colonies; in some the pouches contain but one or two embryos, while 

 in others three is the predominating number. The pouch is attached 

 to the posterior dorsal region of the thorax, a little to the right of the 

 median line, and when fully formed, though still attached to the zooid, 

 it extends posteriorly about as far into the colony as the zooid itself. 



A careful examination of the structure of the pouch shows that it is 

 not merely a diverticulum from the peribranchial sac, but consists of 

 two parts which, for descriptive purposes, may be called the oviducal 

 and the peribranchial portions, though I do not know that they have 

 been developed from the oviduct and peribranchial sac respectively. 

 The oviducal part is a narrow tube, the anterior end of which connects 

 with the oviduct, and the posterior end with the bottom of the pouch. 

 Anteriorly the peribranchial portion is a narrow tube opening into the 

 posterior dorsal corner of the right peribranchial sac. Posteriorly, 

 however, it is enlarged to form the pouch proper, in which the develop- 

 ing embryos are lodged. Figure 8 (Plate 2) represents a young 

 pouch in which the relation of the oviducal (brs. ov'dt.) to the peri- 

 branchial portion (brs. pi'brn.) is shown. Both portions are of course 

 covered by the evaginated ectoderm (ec*drm.). The relations of the 

 stalk of the pouch to the zooid are best shown by means of cross-sections 

 (Plate 2, Figs. 9, 10, 11). The most posterior section (Fig. 9) 

 shows the stalk entirely separated from the zooid and imbedded in 

 the common test. Its oviducal portion (brs. ov'dt.) is seen to be nearest 

 to the part of the zooid containing the oviduct (ovdt.). As the series 

 is followed anteriorly, the ectoderm of the stalk first joins that of the 

 zooid and then the wall of the oviducal portion becomes continuous 



