MUSEUM OF COMPARATIVE ZOOLOGY. 145 
After having found that the cerata arose in close connection with pre- 
ceding ones of the same transverse rows, and therefore ultimately in 
close connection with the first or dorsalmost ceras of each row, it seemed 
desirable to determine the origin of the dorsalmost longitudinal series of 
cerata, and of the origin of new transverse rows. Sagittal, or slightly in- 
clined longitudinal, and also frontal sections of young specimens gave the 
desired information. Figure 16 represents a longitudinal section which 
is not strictly sagittal, the upper edge of the section plane having been 
tilted about 30° towards the right so as to pass at the same time through 
the alimentary tract and the dorsal series of cerata, —the only series 
as yet developed on that side. From the drawing it is clear that the 
alimentary tract sends off diverticula, which pass directly into the first 
cerata of each transverse row. Behind the most posterior ceras the 
mesenchyme is thickened over the alimentary ‘tract, which runs to the 
posterior end of the body. In a section a little removed from this 
(Fig. 17, IL.), one sees the beginning of another papilla behind number 
III. of the series represented, —the foundation of another transverse 
row. The ectoderm has already begun to fold upwards, and the alimen- 
tary tract sends out a prominent pocket. 
Of very great importance is the fact that just behind the Anlage of the 
ceras the testis is arising, so that the mesenchyme which seems to take 
the initiative in the formation of the ceras gives rise also to the sexual 
cells. Moreover, the two cell masses arise close together, and indeed in 
a definite relation to each other. As is clear from an inspection of 
Figure 16, the sexual glands — ovary and testis — lie between the trans- 
verse planes occupied by the cerata, and in each mass the ovary lies in 
front of the testis, so that successive transverse sections cut from the 
head backwards pass in order through a transverse row of cerata, through 
an ovarian mass, and through a testicular mass. This succession is, 
however, not that in which the Anlagen of the three organs have been 
established out of the mesenchyme of the tail end ; for, as Figure 17 in- 
dicates, new sexual cells arise before the ceras which lies in front of them 
begins to appear. 
The oblique (nearly frontal) section, Figure 18, shows the same relation 
of the sexual glands and the cerata. A reconstruction of the series shows 
that diverticula arise from the parts of the alimentary tract indicated by 
the designations cer. I, II., III]., and IV. These diverticula correspond 
in position to transverse rows of cerata. The same reconstruction shows 
that between these diverticula ovary and testis follow in the way just 
described. At the extreme tail end the section passes obliquely through 
