. Analysis of development. Embryology; Embryology. Fig. 66. Behavior of pronuclei in centrifuged eggs of the sand dollar Dendraster. A, Two successive stages (at interval of I/2 hour) of an egg in which a sperm entered at centripetal end, fused with egg pronucleus and the fusion nucleus moved into large centrifugal part of the egg. B, Two successive stages (at interval of 2 hours) of an egg in which a sperm entered at the centrifugal end, failed to unite with egg pronucleus and proceeded to segment the centrifugal end. e. Egg pronucleus; 5, sperm pronucleus; es, fusion nucleus; o, oil cap. (Af
. Analysis of development. Embryology; Embryology. Fig. 66. Behavior of pronuclei in centrifuged eggs of the sand dollar Dendraster. A, Two successive stages (at interval of I/2 hour) of an egg in which a sperm entered at centripetal end, fused with egg pronucleus and the fusion nucleus moved into large centrifugal part of the egg. B, Two successive stages (at interval of 2 hours) of an egg in which a sperm entered at the centrifugal end, failed to unite with egg pronucleus and proceeded to segment the centrifugal end. e. Egg pronucleus; 5, sperm pronucleus; es, fusion nucleus; o, oil cap. (After Moore, '37.) the respiratory quotients, however, show a decrease from about unity in the unfertilized sea urchin egg (Borei, '33) to values vari- ously reported as ranging from to (Ephrussi, '33; Borei, '33; Laser and Roths- child, '39; Ohman, '40) after fertilization. From analyses of lipids Ohman ('44) sug- gests that these represent the chief energy source, whereas from analysis of ammonia liberation Hutchens et al. ('42) suggest oxi- dation of protein. These various investiga- tions have evidently all been carefully per- formed, but it is evidently still necesary to determine to what extent the divergent re- sults are due to technical difficulties and to species differences. Most investigators, how- ever, are in accord with the view that differ- ent substrates are utilized before and after fertilization (see Brachet, '47, for further details). cleavage of the cell. The fact that egg and sperm pronuclei may meet at some distance from the ultimate position of the fusion nucleus does not imply attraction, since it has not been shown that they are diverted from the path that they would take inde- pendently. Wilson ('25) and Morgan ('27) have reviewed the early work on this subject and little has been added since that time. Moore ('37) has studied the movements of the pronuclei in echinoid eggs that had been drawn out into flask-shaped form as a result of high spee
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