64 SPONGES 



individuality, such as Euplectella and many other Hexactinellids, 

 and a few Demospongiae, in which, so far, it is unknown. Discon- 

 tinuous budding, on the other hand, is less common, though 

 sufficiently widely spread in all the main groups. 



The formation of free buds is seen in its simplest forms in the 

 Ascons amongst Calcarea, and in Oscarella amongst Demospongiae. In 

 Ascons a portion of one of the tubes is nipped off as a small spherical 

 reproductive body, as described by Miklucho-Maclay (1868), though arbi- 

 trarily contradicted by Haeckel. In Clathrina buds are formed during the 

 extreme state of contraction when the tubes have become perfectly solid, 

 and the collar cells form a compact mass of rounded cells obliterating the 

 gastral cavity. Tubes while in this condition are often seen to assume a 

 moniliform-headed appearance, and each head or swelling breaks away 

 and becomes a free, solid, reproductive body consisting of an external 

 dermal layer, containing spicules and a central mass of rounded gastral 

 cells. After drifting about for a time the bud fixes itself, expands to 

 form anew its gastral cavity, and then by acquiring an osculum and 

 pores develops into an Olynthiis. In the far less contractile Leucosoleniidae, 

 on the other hand, the reproductive body, formed in an essentially similar 

 manner by becoming nipped off from the extremity of a diverticulum, is 

 always hollow, its thin wall formed from the same elements as the wall 

 of the sponge. It fixes in the same way as the buds of Clathrina, and 

 develops into an Olynthus (Vasseur, 1878). 



In Oscarella, according to Schulze, free buds are formed as papillae 

 protruded from the surface, which become nipped off as little vesicles, 

 each containing ciliated chambers, and surrounded by a flat amoeboid 

 epithelium, which sends out pseudopodia. The vesicle becomes fixed and 

 develops into a little sponge, apparently a minute Rhagon (see p. 125). Of 

 quite a similar type is the formation of free buds in Hexactinellids, the 

 result being the formation of a little Rhagon-like organism (Fig. 76), 

 which in Lophocalyx may acquire an osculum before separation from the 

 parent. In all these cases the bud is produced simply as a separation off 

 of a portion of the body, and contains all the layers and tissues which 

 enter into the composition of the parent organism. In Tethya, however, 

 the budding appears to be of a different type, and is better considered 

 under gemmule formation (see below, p. 67). It is of interest to note 

 that in many sponges with free buds special adaptations exist, derived 

 from the skeleton, for the purpose of extruding them from the parent 

 body. Thus in Lophocalyx (Hexactinellida) the buds are carried outwards 

 from the mother form by long spicules, which finally break off and set the 

 bud free. Similarly in Tethya the reproductive bodies are pushed out by 

 the growth of a long monaxon spicule, on the point of which the bud is, 

 as it were, impaled, and in like manner the buds of Aplysilla are carried 

 outwards on the tip of a spongin fibre. 



The method of propagation by free buds has been successfully 

 imitated in sponge culture by artificial cuttings. The horny sponge of 

 commerce can be propagated in this way, but a considerable time is 

 required for the cuttings to grow into a large sponge. 



