CGELENTEEATA. 17 



Class I. SPONGIA. (Sponges.) 

 AMORPHOZOA. PORIFERA. POLYSTOMATA. SPONGOZOA. 



Fixed aquatic organisms, composed of an aggregate of amoebi- 

 form bodies, etmb provided with a mouth and numerous pores, 

 and including a fibrous framework, strengthened by horny or cal- 

 careous spicules. Larvge free-swimming. 



The gelatinous sarcode forming the animal mass of the sponge 

 is made up of a number of individual masses of protoplasm [plas- 

 tides], forming a thin outer layer and entering deeply into the 

 organism, coating every cavity in the interior. The cavities are 

 connected by canals, which are continuous with ciliated chambers. 

 Minute chambers [pores or ostioles], through which the water 

 passes into the cavities, exist on the outer layer, and the water so 

 admitted is discharged by larger orifices [oscula]. It is to the 

 vibratile action of the cilia that the circulation of the water is 

 due. According to Huxley, the " sponge represents a kind of sub- 

 aqueous city, where the people are arranged about the streets and 

 roads in such a manner that each can easily appropriate his food 

 from the water as it passes along." 



It is doubtful, however, whether the digestion is carried on by 

 the general cells lining the passages or by the ciliated cells. 



By Leuckart and Hackel the canal-system of Sponges is regarded 

 as homologous to the gastrovascular system of the Hydrozoa and 

 the Actinozoa. Furthermore, the Sponges and Corals are regarded 

 as blood-relations, both originating [hypothetically] from a pri- 

 mitive sac [protosaccus], the only morphological character sepa- 

 rating them being the absence of urticating organs in the former. 



Thread-cells are, however, said to be found by Eimer in Reniera 

 [these are by Carter declared to be parasitical polyps]. Eimer 

 also considers that he has established a passage between Sponges 

 and Hydroids. By Carter the relation of Sponges to Ascidians 

 is regarded as greater than to Corals, the latter having only one 

 aperture. 



Reproduction is either as exual by budding &c., or, in the Calci- 

 spongige principally, by ova. According to Huxley, the embryo is 

 " similar to the corresponding stage of a hydrozoon, and is totally 

 unlike any known condition of a protozoon." The ova, so called 

 by some observers, are supposed by Hackel to be spermatozoa, or 

 perhaps vibratile cells. Sponges are also reproduced by gemma- 

 tion. The Grastrula stage is disputed by Barrois and Hyatt. 



According to Saville Kent, " Sponges are compound, colony- 

 building, collar-bearing, flagellate monads, exhibiting neither in 



