Alaska: Insects (Google eBook)

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Doubleday, Page, 1910 - Alaska
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Page 17 - ... less). It is also true of the numerous 6-rayed species of Asterias, Pisaster, and allied genera." On the other hand, the increase of rays is more probably due " to the advantage gained in holding their food securely, and in opening bivalves, than for holding to the rocks, though both go together." " The ability to cling tenaciously to rocks may be perfected in other ways, involving equally an increased number of sucker-feet. This is often attained by lengthening the rays, * * * by crowding the...
Page 389 - Descriptions of new Species of Starfishes and Ophiurans, with a Revision of Certain Species formerly Described.
Page 282 - ... different from the rest and divergent, so as to cover the intervening spaces between the spines, thus forming fascicles or channels for the circulation of water to the papula?.
Page 18 - and may indicate a continuous descent from these ancient forms" (p. 13). He also says, "I am inclined to believe that the increase in number of rays has been due more to the advantage gained in holding their food securely, and in opening bivalves, than for holding to the rocks, though both go together
Page 316 - The aproctous condition, formerly supposed to be characteristic of the family, is unreliable, for in nearly all the genera referred to it there is a perfectly well denned dorsal or "anal" pore, and in some of the genera the pore is even elevated on the summit of a dorsal cone or chimney (Psilaster, Ilyaster, etc.) This pore, which I have designated as "pseudanus...
Page 286 - The various kinds of abactinal ossicles pass into each other by various intermediate forms, so that it is impossible to draw any very strong or sharp family lines on this character alone, though the character of the plating may generally be taken as of generic value.
Page 128 - ... separated from them by a channel, and forming a crowded row of confluent clusters like the dorsals. Dorsal spines small and numerous, in little heaps, which, being confluent in a longitudinal direction, form three or five (according to the distance 272 from the disc) rows, separated from each other by corresponding rows of papuliferous depressions.
Page 297 - ... corresponding vertically ; oblique in the type. No odd interradial plate. Abactinal plates or parapaxillse are regularly longitudinally arranged, of moderate size, somewhat elevated, mostly roundish, covered with a rosette of short, obtuse spinules or granules. When these are removed the plates on the central part of the disk and along the median region of the arms appear as roundish or oval convex bosses. They are connected together by five or six internal radiating ossicles, between which are...
Page 388 - Notes on the Echinoderms of Panama and the West Coast of America, with descriptions of New Genera and Species.
Page 314 - Marginal plates of moderate size, more or less alternate, spiniferous; those of the upper series smaller than those of the lower, rounded, with a central eminence bearing a single large, movable spine, with a group of small spinules around its base. The plates of the lower series may bear two or more similar large spines surrounded by spinules. The upper marginal plates form a narrow margin along the rays. The dorsal surface is covered with small, unequal plates in the form of...

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