236 RITTER. 
EXPLANATION OF PLATE XVI. 
Fic. 48. A longitudinal section of the ganglio-hypophyseal duct at a slightly 
more advanced stage than the one shown in Figs. 44-47. It will be noted that 
here the communication of the duct with the branchial sac, 7.¢.0., the remnant of 
the evagination, is almost closed. The differentiation of the ganglion, 9/., from 
the duct and from the wall of the branchial sac is complete at its anterior end, but 
not at its posterior end. X 720. 
Fic. 49. Cross-section of a duct and ganglion after the ganglion is fully 
separated, but is still very small. X 720. 
Fic. 52. An ovum found alone and free in the body space. X 1200. 
Fic. 55. A multinuecliated mass floating free in the body space ; probably(?) 
an early stage in the formation of a male polycarp. X 508. 
PEROPHORA. 
Fic. 56. Small portion of a colony of P. axnectens almost entirely covering a 
zooid of Clavelina. The specimen is the fully compounded variety, and forms a 
thin encrusting layer on the surface of the C/avelina. The tips of the stolons, s/o., 
and young buds, éd., are shown at the margin of the colony. Not camera. X 2. 
Fics. 57-64. From aseries of transverse sections extending from before back- 
ward of P. aznectens, illustrating the method by which the bud is connected to the 
stolonic partition by its left peribranchial sac. The point of connection is seen in 
Fig. 60. X 138. 
Fic. 65. Transverse section of a P. Listeri bud, slightly more advanced in 
development than the preceding ; illustrating, likewise, the connection of the left 
peribranchial sac to the stolonic partition. In this section, however, the series 
passes from behind forward, so that the apparent reversal of right and left does 
not occur. X 138. 
Fic. 66. Shows a case in which the zooid is fully separated from the stolon. 
This is the section of a complete series in which the stolon approaches most 
closely to the bud, but here the separation is complete. P. azmectens. X 210. 
Fics. 67 and 68. Show the development of the pericardial vesicle. Fig. 67 
shows its position with reference to the point of attachment of the inner vesicle to 
the stolonic septum. Both are from the same series of sections. PP. annectens. 
Fig. 67, X 72; Fig. 68, X 330. 
Fic. 69. A later stage in the formation of the pericardium, but still before its 
separation from the endoderm. X 720. 
Fic. 70. From the same series as the last to show the relation of the 
forming pericardium to the point of attachment of the stolonic septum to the 
primitive inner vesicle. X 120. 
Fic. 71. A condition of the pericardium similar to that shown in Fig. 69, but 
slightly more advanced in development. X 500. 
