GONADS OF CEPHALODISCUS NIGRESCENS. 45 
p. 412, footnote) compares with the chordoid structure which he found to exist 
(22, p. 305) in the mid-ventral wall of the stomach of Actinotrocha. 
From all this it would appear to an unprejudiced mind that the gut-wall may 
develope tracts of vacuolated skeletal cells in any part of its extent, and that, 
except in the case of the notochord of the Cephalochorda and Vertebrata, which 
occupies a definite position between the central nervous system and the enteric 
tube, any close comparison of these various tracts in the different forms of the 
Chordata is almost impossible. 
The suggestion of Masterman (22, p. 356, and 25, p. 915) that the pleuro- 
chord of Cephalodiscus is a skeletal structure developed in the wall of the pharynx 
for the purpose of keeping open the gill-cleft, and Willey’s remark (34, p. 238) 
that a long pleurochord may mark the position of a row of obliterated gill-slits, 
are worthy of careful consideration. In the Cephalochorda, Cyclostomata, Fishes, 
and Amphibia, the positions between the gill-slits are supported by skeletal tissue 
(mesoblastic, it is true, whereas the pleurochord is hypoblastic), and it is not 
unreasonable to suppose that the long pleurochord of Cephalodiscus, with the 
gill-slit at its anterior end, may represent the skeleton of a series of slits, only 
one of which now appears in ontogeny; and further, that in Actinotrocha 
(Masterman, 22) and Rhabdopleura (Schepotieff, Bergens Mus. Aarbog, 1904, p. 14, 
Kiemenrinne) the skeletal matter of the slit develops (‘liver d verticula” of earlier 
writers (Masterman, 22, p. 304)), although the slits themselves never make their 
appearance. Willey claims that the lateral pouches of the stomochord of the 
Enteropneusta are the “ persistent vestiges of primitive gill-clefts belonging to that 
portion of the body which, in the Enteropneusta, is now specialised as the collar 
region” (34, p. 238). 
Gonads. 
The individuals of the species under consideration possess either two ovaries or 
two testes, or an ovary and a testis. In a series of thirty-six individuals examined, 
fifteen had two ovaries, seven two testes, and fourteen an ovary and a testis. The 
three kinds of individuals are not restricted in their distribution. The same branch 
of the colony may have male, female, and hermaphrodite individuals, and no 
distinction. can be drawn as regards sex between the individuals found in the basal, 
middle, and more terminal portions of the same branch of the colony. 
If the gonads are large they bulge somewhat upon the sides of the body, and 
by stretching the pigmented body-wall that covers them, cause it to be paler than 
the other parts of the surface (see figs. 7 and 8, plate 3). 
The ovary is narrow at its anterior extremity, where it opens upon the exterior 
by a short duct with a small, frequently ill-defined cavity, and with walls of a red 
colour, which resembles that of-the red line in the buccal shield in tint and in being 
