Quarterly Journal of Microscopical Science, Vol s3-100, 557-570, Copyright © 1959 by Company of Biologists

Spicule Growth Rates in Leucosolenia variabilis

¹ Department of Zoology, University College of North Wales, Bangor

The growth rates of spicules of Leucosolenia variabilis have been determined by photographing stretched pieces of the wall for a maximum period of 17 h. For 3 pieces, A, B, and C, the average rates for spicule rays above 25 µ in length were respectively 2.50 (18-21° C), 1.64 (18° C), and 1.29 (17° C) µ per h. The discrepancies are greater than would be expected from the differences in temperature.

For both basal and oscular rays the growth rate increases to a steady level as the rays lengthen. The basal rays grow precociously at first, but in A the oscular rays soon caught up with the associated basal ray, while in B and C (both derived from the same oscular tube) the oscular rays of the growing spicules tended to remain smaller than the associated basal ray during the recorded period of growth. Whether this difference between the pieces was due to genetic factors or to the experimental conditions was not determined.

Above 25 µ in length the oscular and basal rays grow at similar rates, regardless of whether the rays belong to Y-, T-, or even aberrant spicules. The orientation of the optic axis of the mineral constituent has thus no appreciable effect on the growth rate.