Contributions from the Zoological Laboratory, Volumen12Published for the University of Pennsylvania, 1906 Vols. for 189 --1956-58 are reprinted from various scientific journals. |
Otras ediciones - Ver todas
Términos y frases comunes
4-cell stage adult Aiptasia animal ascidian ascidian egg behavior blastomeres blastopore body branchiæ bundles capillary caudal Chabry changes chitin chorda cells cirri cirrus clear protoplasm cleavage color cone cells corneal pigment cells cytoplasm diameter differentiation disk distal dorsal dorsal view Driesch ectoderm elongated elytra endoderm endoderm cells entire fibres gastrula give rise gray crescent groove injured invagination larva larvæ lateral layer left half length lobes localization middle muscle cells nearly nerve neural plate neuropodial neuropodium normal notochord notopodial notopodium nuclei occur ommatidia ommatidium oöplasmic oöplasmic substances organism pair papillæ parapodia parapodium PHOTO physiological portion position processes prostomium protoplasm pupa quadrants quarter embryos reaction region retinula retinular cells rhabdome right or left rows segments sense spots seta setæ showing shown in Fig side slender slightly somites species specimens sperm surface tapering tentacles thoracic tion transverse tuft usually ventral yellow crescent
Pasajes populares
Página 260 - ... easily studied of the processes of the organism, and it is clear that these processes are closely connected with, and are indeed outgrowths from, the more recondite internal processes. There is no reason for supposing them to follow laws different from those of the other life processes, or for holding that regulation in behavior is of a different character from that found elsewhere.
Página 74 - Twelve pairs of elytra are borne on somites II, IV, V, VII, IX, XI. XIII, XV, XVII, XIX, XXI, and XXIII.
Página 220 - ... of harmonizing the facts of cytoplasmic organization with the nuclear inheritance theory. TYPES OF GERMINAL ORGANIZATION. By those who maintain the view that the egg is typically composed of " simple undifferentiated protoplasm " the remarkable organization of the ascidian egg will probably be regarded as an extreme case of precocious differentiation.
Página 194 - The development of ascidians is a mosaic work because there are definitely localized organforming substances in the egg; in fact the mosaic is one of organ-forming substances rather than of cleavage cells. The study of ctenophores, nemertines, annelids, mollusks, ascidians and amphibians (the frog) shows that the same is probably true of all these forms and it suggests that the mosaic principle may apply to all animals (p.
Página 1 - We do not need any purpose or idea in the mind of the organism, or any "psychoid" or entelechy, to account for the change of behavior, for an adequate objective cause exists. We know experimentally that the darkness or the lack of oxygen interferes with the metabolic processes. This very interference is then evidently the cause of the change of behavior.
Página 3 - The essential fact is that interference with the internal processes causes a change in behavior. The mere fact of a change under these conditions tends in itself to be regulatory. The original behavior has brought on the interfering conditions, hence the best thing to do is to change this behavior. If the unfavorable condition still continues the behavior is changed again; this being continued, the organism is bound to escape from the interfering condition if it is possible to do so. In some cases...
Página 12 - Neither of these principles seem to contain anything specifically vitalistic, or opposed in principle to what we find in the inorganic world. Is it possible that regulation is based on similar principles in other fields than behavior? Bodily movement is only one of the many kinds of activity that may vary, and variations of any of the organic activities may impede or assist the physiological processes of the organism.
Página 194 - Under experimental conditions . . . . they develop, if they develop at all, into the organs which they would normally produce; and conversely, embryos which lack these substances, lack also the organs which would form from them. . . . . Three of these substances are clearly distinguishable in the ovarian egg and I do not doubt that even at this stage they are differentiated for particular ends (p.
Página 258 - 04 — On the Habits and Reactions of Sagartia Davisi. Biol. Bull., vol. 6, no. 5, pp. 203-216. EXPLANATION OF PLATES Puvrr 1 Fig.
Página 211 - ... and extending a little above the equator, while the clear protoplasm is located chiefly in the upper hemisphere. The dark gray portion of the vegetal hemisphere gives rise to the endoderm of the larva, the light gray crescent to the notochord and neural plate.1 All the principal organs of the larva in their definitive positions and proportions are here marked out in the 2-cell stage by distinct kinds of protoplasm...