. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. 64 BIOLOGICAL Conklin (4) was the first to call attention to the possible importance of the sphere-substance in the cleavage of the Q.^%. He summarizes his results on the Qg^ of Crepidiila thus : "After the first two cleavages the sphere-substance is differently dis- tributed to the different cells, the entire sphere-substance of one generation always going into those cells of the next genera- tion which lie nearest the animal pole. This differential distri- bution of the spheres
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. 64 BIOLOGICAL Conklin (4) was the first to call attention to the possible importance of the sphere-substance in the cleavage of the Q.^%. He summarizes his results on the Qg^ of Crepidiila thus : "After the first two cleavages the sphere-substance is differently dis- tributed to the different cells, the entire sphere-substance of one generation always going into those cells of the next genera- tion which lie nearest the animal pole. This differential distri- bution of the spheres has been followed through every cleavage up to the twenty-four-cell stage. As the form of the cleavage is perfectly constant, it follows that the sphere- substance of any genera- tion goes into certain definite cells which have a perfectly constant origin and destiny. This differ- ential distribution of the spheres is not caused by ,, , , ^ , . r , their specific weight, since 1"IG. 20. — Unio. r irst cleavage ; the elongation of the ^ o ' sphere-substance in the larger cell and of the cell their mOVemeUtS arC thc itself marks the plane of the second cleavage. In a . , . slightly later stage there is a well-marked constriction SamC m WhateVCr pOSltlOU across the cell in the position of the future second thg cq\\ maV be nlaCPd Tt cleavage-spindle in this cell. seems to be the result of a form of polarity which, like that of the ^gg itself, is not the result of gravity. "The centrosomes do not, apparently, arise from the sphere- substance of the previous division, but some distance from it, and the sphere-substance never divides, but each sphere ulti- mately grows ragged at its periphery and gradually fades out into the general cytoplasm. "The differential distribution of the spheres and their subsequent conversion into cytoplasm suggest that they may be important factors in the differentiation of cleav- age cells, and if further investigation should establish th
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Keywords: ., bookcentury1800, bookdecade1890, bookpublishe, booksubjectbiology
