ON PENNELLA BALAINOPTERZ. 419 
ALIMENTARY CANAL. 
The canal extended in a direct line from mouth to anus, and had no convolutions in 
any part of its course. ‘The oral cleft passed deeply into the substance of the ventral 
surface of the head, and was continued at its lower part into a relatively wide cesophagus, 
down which a bristle could readily be passed. 
In transverse sections through the upper part of the cesophagus, the diameter from 
side to side was seen to be much greater than in the dorsi-ventral direction, and the 
opposite walls were almost in contact. The ventral wall of the canal was in close rela- 
tion with the capsule of the mid-ventral space of the ccelom, which lay between it and 
the chitinous wall of the head, the dorsal wall was in relation to the musculature of the 
head, and the sides were in contact with the cesophageal ganglia (fig. 8). 
In the lower part of the head, where the muscular fibres were replaced by areolated 
tissue, the dorsal wall of the canal was separated from the chitinous envelope by the 
dorsal space, which contained a granulated material, possibly a coagulum. The space 
was bounded by a fibrous membrane, which was lined by nucleated cells, though 
frequently they were in patches and did not form a continuous layer. These cells were 
about the size of leucocytes, and not unlike them in appearance. The muscular wall of 
the alimentary canal was attached to the areolated tissue at its sides by bands, formed 
of connective tissue and non-striped muscle, which constituted short lateral mesenteries ; 
between these bands were narrow channels, in which blood or other nutritive fluid may 
have circulated. 
Transverse sections through the body immediately below the arms showed the 
alimentary canal in the axis of the section, with a space in relation to both its dorsal 
and ventral surfaces. The lumen of the canal was not so compressed dorsi-ventrally as 
in the head. Well-marked areolated tissue surrounded the canal with its dorsal and 
ventral spaces, and closely packed the whole area between them and the inner surface of 
the chitinous wall (fic. 9). As it ethciently supported the canal, the lateral mesenteries 
were short and their fibres were continued into the meshwork of the areole, which 
again was continuous with the membrane lining the inner surface of the wall. A few 
scattered pigment cells were seen in this membrane, though not nearly so abundant 
as lower down in the thoracic segment of the body. 
In sections through the attenuated thoracic segment the areolated tissue was 
no longer present, and the space inclosed by the chitmous wall was occupied by the 
alimentary canal and the dorsal and ventral spaces. The canal was in the axis of the 
section and was reniform in shape; its lateral angles were in such close relation to the 
lining membrane of the chitin that the mesenteries were practically absent (fig. 16). The 
dorsal and ventral spaces were proportionally large, almost equal in size, and were situ- 
ated between the lining membrane and the corresponding wall of the alimentary canal. 
Hach space was inclosed by a definite wall of fibrous membrane, the inner surface of 
which was lined by a layer of nucleated cells; the cell-plasm in some was granular 
