227 
very thin, but the entoderm is as thick as in the bodywall. The connecting septum is short, 
broad and irregular. 
Actinopharynx. The wall is folded at the connective points of the mesenteries; the 
folds at the sagittal ends oi the slit-like lumen widen in the lower part of the actinopharynx. 
The ectoderm contains a large number of actinopharyngeal glandcells but not many others. 
The upper part of the actinopharynx has no pigment but in the lower part a brown pigment 
is found in rather a large quantity, but not so large as to cover the structure of the epithe¬ 
lium. There is no lip. The mesogloea is very thin; the entoderm is of the same structure 
as in the bodywall, and it contains slightly developed circular musclelibres. 
The mesenteries are of normal number. Their entoderm is 26 p, their mesogloea 4 p. 
The course, which the pairs of secondary mesenteries take, is rather curious ; in the toppart of 
the oral cone these mesenteries extend from the bodywall to the actinopharynx but lower 
down they leave the bodywall and extend between the actinopharynx and a lateral fold of the 
actinopharynx (PI. VI, fig. 13). — There is a mesenterial musclesystem ; I was obliged, through 
the incompleteness of the series ol sections, to make out the system from several sections. 
In horizontal sections through the basal part of the oral cone, at the lowest part of the 
actinopharynx, one of the secondary mesenteries shows its longitudinal musclefibres in that 
part, which is nearest the actinopharynx, while in the same section that part of the same 
mesentery, which is nearest the bodywall shows its transversal musclefibres at the other side. 
For this reason the following system of longitudinal musclefibres is a little dubious. On one 
of the sagittal primary mesenteries I saw musclefibres at the side turned towards the other 
mesentery of the same pair. — On both the primary transversal mesenteries they are found at 
the same side; one of the pairs of secondary mesenteries has its longitudinal fibres turned 
towards the primary transversal ones, while the other pair has those fibres on the side averted 
from these transversal mesenteries. 
The mesenterial filaments are straight along the primary sagittal mesenteries, but 
convoluted along the primary transversal mesenteries. They contain pigment. 
Reproductive organs. There are only testes to be found in the primary transversal 
mesenteries. The testes are oval with a longest diameter of 120 p. Each is surrounded by a 
very thin mesogloeal capsule, much less than 1 p thick. All the testes are in the same stadium; 
they are ripe and filled with a bundle of spermatozoa, surrounded by spermatocytes. The heads 
of the spermatozoa are spread out fan-shaped, while the ends of their tails are crowded 
together. The tails in all the testes of an entire mesentery are turned in the same direction 
(PI. VI, fife- 1 3 )i vlz - towards the mesenterial mesogloea. — Further it is to be remarked that 
the testes are found on one single side of the mesentery, which is unilaterally swollen; so the 
mesentery is usually S-shaped (fig. 261 A). I have noticed the same fact with the ovaria of 
other species (cf. the primary transversal mesenteries and also the secondary mesenteries in 
PI. V, fig. 7). In his schematical figures Brook draws a bilateral swelling of the fertile mesen¬ 
teries, but this may be explained by the mesogloea not always being easily distinguished in 
these mesenteries. The mesogloea is not rectiliniarly stretched as in fig. 261 B, but the pseudo¬ 
bilateral swelling may be explained with a unilateral one as in fig. 261 A, but to such a degree 
