[443] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 149 
pale orange-brown, becoming lighter colored as they expand. On the 
lower side the spots are more scattered, but the intervals are generally 
less than the diameter of the spots. On the upper side the spots are 
much crowded and lie in different planes, with the edges often over- 
lapping, and thus increasing the variety of the tints. Along the middle 
of the back the ground-color is pale flesh-color, with a median dorsal 
band, along which the spots are tinged with green, in fine specks. Above 
each eye there is a broad lunate spot of light purplish red, with smaller 
brown spots. The upper surface of the head is deeply colored by the 
brown spots, which are here larger, darker, and more crowded than else- 
where, and situated in several strata. The arms and fins are colored 
like the body, except that the spots appear to be smaller. The suckers 
are pure white. The eyes are dark blue-black, surrounded by an irides- 
cent border, and in this genus the eves are provided with distinct lids. 
In this respect, Ommastrephes differs from Loligo, for in the species of the 
latter genus, the integument is continued directly over the eye, the part 
covering the eye being transparent. 
Most of the higher Gastropods inclose their eggs in capsules, which 
they attach to stones, alge, or shells, and within these the eggs hatch 
and the young have a well formed shell before they eat their way out of 
the capsules, and when free they crawl about by means of the ‘ foot,” 
like the adult. But in the lower orders of Gastropods most of the young, 
when first hatched, are furnished with vibrating cilia and swim free, by 
this means, for a short time. These larve are very different from the 
adults, andin case of the naked mollusks (Nudibranchs) the larvee are 
furnished with a beautiful, little, glossy, spiral shell, which they after- 
wards lose. 
The Pteropods swin free in all stages. The young and adults swim by 
means of two wing-like appendages, developed on each side of the neck, 
which may be compared to the anterior lateral lobes of the foot, seen in 
AXolis, (fig. 174,) and many other Gastropods, if we suppose these to 
become enormously enlarged, while the rest of the foot remains in a rudi- 
mentary or undeveloped condition, often serving merely for the attach- 
ment of the operculum. 
The Styliola vitrea (Plate XXV, fig. 178) was taken in the day-time 
at the surface, September 8, among Salpa, off Gay Head. Its shell 
is a thin, white, transparent, glassy cone, about a third of an inch long 
and slightly curved toward the tip. The animal is also white. The 
Spirialis Gouldii has a delicate, white, transparent, spiral shell, when 
adult having seven whorls, which turn to the left. The shell is marked 
by very fine revolving lines, visible only under the microscope. This 
species is seldom met with at the surface in the day-time, but is often 
abundant in the early evening. According to the observations of Mr. 
A. Agassiz, in confinement they rarely left the bottom of the jars dur- 
ing the day, merely rising a few inches and then falling again to the 
bottom. After dark they became very active, swimming actively near 
