TYPE PROSOPTOIA. 261 



bodies, as in FredericeUa, or formiug compact masses, as in 

 Alcyonella arid Lophopus, or even being capable of motion, as 

 in Cristatetta. In some forms, e.g. Lophopus, the ectocjst pos- 

 sesses a gelatinous consistency, though usually it is chitinous, 

 and the various zooecia are in free communication with one 

 another, not being separated by transverse partitions. 



In addition to multiplying by the usual processes of bud- 

 ding and by ova, the Phylactolsemata develop upon the 

 fuuiculus special internal buds, termed statoblasts, which are 

 enclosed within dense chitiuous capsules. These are set free 

 by the dying and disintegration of the parent and, being pro- 

 tected by the resistant capsule, retain their vitality under 

 conditions, such as cold and dryness, that destroy the adult 

 individual. They are evidently a special provision for the 

 perpetuation of the species developed in accordance with the 

 fresh-water habitat, in which the organisms are exposed to 

 various conditions not apt to be met with in the ocean ; it is 

 interesting to note in this connection the occurrence of gem- 

 mules in the fresh-water sponges which are strictly compara- 

 ble to the statoblasts and have a similar significance. 



2. Suborder Gymnolcemata. 



The Gymnolaemata are distinguished from the Phylactolre- 

 mata by being, with the single exception of the genus Paludi- 

 cella, marine in habitat, by the tentacles being arranged in 

 the form of a circle, and by the invariable absence of an epi- 

 stome. 



As in the Phylactolsemata, the colonies vary greatly in 

 form, being in some cases encrusting, Membranipora, Flus- 

 t/'ii, in others branching, Scrupocettaria, or in others again 

 massive, Alcyomdium ; and furthermore the ectocyst pre- 

 sents varying degrees of consistency, being frequently chitiu- 

 ous, but occasionally somewhat gelatinous or calcified to a 

 greater or less extent. The zooecia are not in free communi- 

 cation with each other, but each is closed below or posteri- 

 orly by a transverse chitiuous plate in which perforations are 

 said to be present, though doubt has recently been thrown 

 upon their existence as perforations. In shape, too, the 

 zooecia like the colonies vary greatly, especially so far as their 



