ACALEPH &. 109 
tains cells which are full of air. Above, this disc is covered by the 
integument alone; below, it sustains all the parts of which the 
[compound] animal consists. 
[The shell of Velella with its horizontal and perpendicular plates 
consists of a single piece. The thicker horizontal portion is formed 
of two laminz connected by perpendicular concentric pieces, so that 
annular canals are formed which are filled with air. These canals 
communicate with each other in Velella, but not in Porpita: in both 
they open externally by many minute pores on the upper surface. 
The soft parts constitute a mantle which covers the shell and projects 
beyond its edge by a free border. At the inferior excavated portion 
of the shell, the mantle has on its outside the attached polyps and 
appendages, on the inside the large liver. 
The polyps are of two sorts, a single large and central polyp, and 
many small ones disposed around it in irregular rows. They have 
been designated “stomachs” and “suctorial tubes.” But observers 
do not agree respecting their function. Lesson attributes to both sets 
a digestive power, Voyage de la Coquille, pp. 49—56, and Acaléphes 
p- 661: whilst V. Sresotp Verg/. Anat. s. 63, note, thinks that the 
smaller polyps alone discharge the office of digestion, and consigns 
the large one to the respiratory system: and Hotutarp Ann. des Se. 
Nat. T. m1. 1845, p. 250, says that the large central pouch is the 
stomach and the small ones canaua aquiferes. KOELLIKER however 
assures us that he has found small crwstacea both in the large and 
the small tubes, and has seen the residue of digestion pass from 
them all indifferently. Consequently we conclude with him and 
others, that the Velellide are colonies or compound animals. 
The liver is a large brownish mass placed above the central 
stomach : it fills the inferior cavity of the horizontal plate. It is a 
collection of fine canals formed of homogeneous membrane lined 
with brown cells. A certain number of the canals branch from two 
openings in the base of the central polyp: they frequently anastomose 
and form a network on the surface of the liver from which fine 
vessels pass to the perpendicular plate and to the margin of the 
horizontal plate (Velel/a). These vessels, then, would seem to have 
received the nutriment which has passed from the central stomach 
into the liver-canals, for the purpose of redistribution to the soft 
parts when it has been modified by the biliary secretion. Of the 
smaller polyps a few, which hang beneath that part of the liver which 
projects beyond the large polyp, open into liver-canals: but the 
