INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 443 



pale orauge-brown, ijecoming 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 iiesh-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 tins 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 eyes are provided with distinct lids. 

 In this respect, Ommastrephes differs from Loligo, for in the species of the 

 latter genus, the integument is continued directl}^ 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, alg?e, 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 larvae are very different from the 

 adults, and in case of the naked mollusks (^udibranchs) the larvse are 

 furnished with a beautiful, little, glossy, spiral shell, which they after- 

 wards lose. 



The Pteropods swim 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 

 iEolis, (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 Sti/Uola vltrea (Plate XXY, fig. 178) was taken in the day-time 

 at the surface, September 8, among Salpcc^ off Gay Head. Its shell 

 is a thin, white, transparent, glassj^ cone, about a third of an inch long? 

 and slightly curved toward the tip. The animal is also white. The 

 Spiriaus Gouldn 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 



