LANCELETS. 
559 
tentacles, growing from the margin of the hood-like expansion of skin which 
surrounds the mouth. The notochord extends to the anterior and posterior 
extremities of the body, reaching beyond the muscle-plates, and likewise in advance 
of the front extremity of the overlying nerve-chord; the latter feature being 
peculiar to the lancelet. An aperture distant about two-thirds of the whole length 
from the head, and opening in the middle line of the lower surface of the body, is 
the outlet of a large cavity, or atrial chamber, surrounding most of the internal 
organs, and especially the large pharynx; and the vent, as in many tadpoles, is 
situated high up on the left side, near the hinder end of the body. The reproduc¬ 
tive organs, which form oval structures lying below the muscle-plates, differ from 
those of the Vertebrates in that they consist of a large number of perfectly distinct 
chambers, corresponding to the muscle-segments of the region of the body along 
which they extend. In connection with the fins, it should be observed that, except 
at its two extremities, the dorsal fin is supported by a series of gelatinous rays, each 
lying in a chamber of its own; while the ventral portion of the caudal fin has a paired 
series of similar supports. In young and transparent examples, the pharynx, or that 
portion of the alimentary tract immediately behind the mouth, is distinctly visible 
through the walls of the body, and can be seen to be perforated on each side by a very 
large number of vertical gill-slits, opening into the atrial chamber. In the living 
creature an almost continuous current of water is drawn, for the purpose of breath¬ 
ing and feeding, through the mouth into the pharynx, whence it escapes by means of 
the gill-slits into the atrial chamber, from which it is discharged through the pore. 
Unlike even the lowest Vertebrates, lancelets have no cartilaginous skull; the only 
solid structure in the head taking the form of a ring of cartilage in the hood surround¬ 
ing the mouth, which gives off a series of processes for the support of the feelers. 
Although paired eyes, as well as organs of hearing, are totally wanting in these 
strange little creatures, a pigment-spot at the front end of the nerve-tube represents 
a median eye; behind which is a small nasal pit, communicating in the larva by 
means of a small pore with the front of the nerve-tube. With regard to the other 
soft-parts, it will suffice to mention that the anterior extremity of the nerve-tube 
is not expanded to form a true brain; and that the heart is represented merely by 
a series of pulsating dilatations of the great blood-vessel; the blood itself being 
devoid of colour. 
Lancelets are represented by some eight or nine species, all of which may be 
included in a single genus; although one from the Bahamas is peculiar on account 
of the unsymmetrical arrangement of its reproductive organs. Essentially littoral 
forms, inhabiting shallow water, especially where the bottom is sandy, these 
creatures have an almost universal distribution on the temperate and tropical 
coasts, although they are often curiously local. The European form has been 
recorded from Scandinavia, Heligoland, the English Channel, France, tire Medi¬ 
terranean, and Chesapeake Bay, growing to an unusual size in French waters. 
Other species occur on the Atlantic and Pacific shores of North and South 
America, as well as on the coasts of Australia, Japan, Ceylon, and the Fiji Islands. 
Mr. A. Willey remarks that the lancelet “ possesses an extraordinary capacity for 
burrowing in the sand of the seashore or sea-bottom. If an individual be dropped 
from the hand on to a mound of wet sand, which has just been dredged out of the 
