In Leucosolenia botryoides[[256]] Vasseur describes a similar process; in this, however, a strikingly distinctive feature is present (Fig. 114), namely, the buds have an inverse orientation with respect to that of the parent, so that the budding sponge presents a contrast to a sponge in which multiplication of oscula has occurred. In fact, the free distal end of the bud becomes the base of the young sponge, and the osculum is formed at the opposite extremity, where the bud is constricted from the parent.
Fig. 113.—Lophocalyx philippensis. The specimen bears several buds attached to it by long tufts of spicules. (After F. E. Schulze.)
Fig. 114.—Leucosolenia botryoides. A, a piece of the Sponge laden with buds, a-f; i, the spicules of the buds directed away from their free ends; k, the spicules of the parent directed towards the osculum, j. B, a bud which has been set free and has become fixed by the extremity which was free or distal in A. (After Vasseur.)
Such a reversal of the position of the bud is noteworthy in view of its rarity, and the case is worth reinvestigating, for in other animal groups a bud or a regenerated part retains so constantly the same orientation as the parent that Loeb,[[257]] after experimenting on the regeneration of Coelenterata and other forms, concluded that a kind of "polarity" existed in the tissues of certain animals.
In Oscarella lobularis[[258]] the buds are transparent floating bladders, derived from little prominences on the surface of the sponge. Scattered in the walls of the bladders are flagellated chambers, which open into the central cavity. The vesicular nature of the buds is doubtless an adaptation, lessening their specific gravity and so enabling them to float to a distance from the parent.
Gemmulation.—Spongilla has already afforded us a typical example of this process. Gemmules very similar to those of Spongilla are known in a few marine sponges, especially in Suberites and in Ficulina. They form a layer attached to the surface of support of the sponge—a layer which may be single or double, or even three or four tiers deep. A micropyle is sometimes present in the spongin coat, sometimes absent; possibly its absence may be correlated with the piling of one layer of gemmules on another, as this, by covering up the micropyle, would of course render it useless. Presumably when a micropyle is present the living contents escape through it and leave the sponge by way of the canal system (Fig. 115).
Fig. 115.—Gemmules of Ficulina. A, vertical section of gemmules in situ; B, vertical section of upper portion of one gemmule. m, Micropyle.