PORIFERA 



completely flagellated larva; its archaeocytes are internal (as in 

 Sycon) ; future dermal cells, recognisable as such, are absent. 

 They arise, as in G. Uanca, by transformation of flagellated cells ; 

 but (1) this process is confined to the posterior pole, and (2) the 

 internal cavity is small and filled up with archaeocytes. Con- 

 sequently the cells vfhich have lost their flagella and become 

 converted into dermal cells cannot sink in as in C. Uanca : they 

 accumulate at the hinder pole, and thus arises a larva half 

 flagellated, half not ; in fact, an amphiblastula. Or, briefly, 

 in Zeucosolenia the larva at hatching is a parenchymula, and 

 vv'hen ready to fix is an amphiblastula ; and, again, the differ- 

 ence between tlie newly hatched larva and that of Sycon is due 

 to the earlier occurrence of cell differentiation in the latter. 

 What completer transitional series could be desired ? 



Turning to the Micromastictora, the developmental history 

 already sketched is fairly typical (p. 172). The differences 

 between Mega- and Micro - mastictoran larvae are referable 

 mainly to the fact that the dermal cells in the latter become 

 at once differentiated among themselves to form the main types 

 of dermal cell of the adult.'^ The metamorphosis is comparable 

 to that of C. Uanca. Among Tetractinellida and Hexactinellida 

 sexually produced larvae have not been certainly identified. 



Asexual reproduction takes place according to one of three 

 types, which may be alluded to as (1) "budding," (2) "gemmula- 

 tion," (3) formation of " asexual larvae." 



By budding (Pig. 113) is meant the formation of reproductive 

 bodies, each of which contains differentiated elements of the 

 various classes found in the parents A simple example of this is 

 described by Miklucho Maclay in Ascons, where the bud is 

 merely the end of one of the Ascon tubes which becomes pinched . 

 off and so set free. 



In Zeucosolenia hoiryoides ^ 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. Such a reversal 



1 Maas, Zool. Gentralbl. v. 1898, p. 581. '^ Arch. Zool. Exp. viii. 1879, p. 59. 



