• Volume 67, Issue 6

      June 1968,   pages  247-298

    • Patterns of reproductive periodicities in four species of indo-pacific echinoderms

      J S Pearse

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      1. Four species of Indo-Pacific echinoderms, the echinoidsDiadema setosum andEchinometra mathaei, the asteroidLinckia laevigata and the holothuroidHolothuria atra, are reproductively active and spawn more or less continuously, when they occur near the equator.

      2. Gametogenesis is synchronous among individuals ofD. setosum, and spawning occurs rhythmically, probably more or less monthly, during the spawning period. This spawning rhythm does not seem to be related to lunar phases as previously reported. When further than 10–15° latitude from the equator, reproductive activity becomes more and more restricted, until at about 30° latitude the spawning period is limited to the summer months.

      3. Gametogenesis is asynchronous among individuals ofE. mathaei, L. laevigata andH. atra, and different individuals spawn at different times during the spawning periods. Some individuals ofE. mathaei are reproductively active at all times of the year throughout most of its distribution, except when north of about 27° N. latitude when reproductive activity is limited to the summer months.

      4. Sea temperature seems to be important in regulating the reproductive periodicities of at least two of the species.D. setosum is reproductively active when the temperatures are above about 25° C., andE. mathaei is reproductively active when the temperatures are above about 18–20° C.

    • Joints in relation to structural history, Anantagiri Hill ranges, Visakhapatnam district, Andhra Pradesh

      R V R Rau G Krishna Rao

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      Attitudes of about 4,000 joints from Precambrian rocks (1,490±200 my.) in the Anantagiri Hill ranges reveal that the joint sets are systematically distributed. The joint sets could be related to the fold and fault movements. The different joint systems recorded are the result of a stress system acting in NW-SE.

    • Some aspects of the pre-vindhyan formations of the Son Valley, M.P.

      S Lakshmanan

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      The paper gives a general account of the stratigraphic position of the granite seen in the Son Valley, and also the age, extension, folding, uplift, and denudation of the Bijawars. The author’s study has led him to conclude that the granite is of post-Bijawar age, and that the Bijawars of the Son Valley show resemblance to the Bijawars of the type area, the only difference being that the Son Valley Bijawars are more disturbed and metamorphosed with the obliteration of sedimentary characters. The absence of any evidence for glaciation during Bijawar times is also pointed out.


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