476 
PROTOZOA. 
sent a very complex appearance, when the individuality of the single ^^sponge- 
person ” is almost annihilated through the formation (by gemmation, fission, 
or coalescence) of sometimes very intricate communities, in which the rami- 
fied and convoluted interstitial channels ” (though recognizable by being 
always without endoderm) imitate in a deceptive manner the true gastral 
channels of the Leucones. Sometimes pseudogasters,” pseudostomes,” and 
“ pseudopores,” or ‘‘pseudostia ” are developed ; and these have often been 
confounded with the true mouths,” stomachs,” ostia,” &c., both in cal- 
careous and siliceous sponges, under the name of “ afierent ” and “ efferent ” 
tubes, pores, &c. — denominations which are therefore utterly rejected by the 
author. 
Eimku (10), in a species of Roniera (from Capri), has found thread-cells 
(the absence of which is, according to Iliickel, the only character separating 
sponges from Cvdenterata) abundantly, developed or in course of develop- 
ment, single or in small heaps, dispersed through the sarcode, gathered around 
the spicula and the afierent pores, and especially investing the walls of the 
stomach,” but never on the external surface. In a second species (allied 
to Reniera Jihulata and Desmacella vagahunda), living on crabs, he found 
them likewise in all stages of evolution investing the channels opening into 
the oscula, but none on the external surface. In a third species or variety, 
however, which occurs with the preceding, and has the same external ap- 
pearance, well developed thread-cells were only found sparingly, but plenty 
in various stages of evolution ; and in a fourth variety (agreeing partly with 
R. informis and accommodatd) a different kind of thread-cells was found, dis- 
persed through the whole sponge, but not investing the inner surface of the 
efferent tubes : some specimens had only the earlier stages ; in others none 
were found j and the same negative results were observed from the exami- 
nation of numerous other species of Reniera^ occurring in company with 
the cnidophorous species, and only to be distinguished from these by the 
shape of the spicula. Eimer is nevertheless convinced that these thread- 
cells could in no way have been introduced from without. The value of 
these observations a})pears, however, to bo diminished by an observation of 
(^AitTiai (fi), wlio, puzzled at first by detecting many thread-cells in the 
internal parenchyma of a digito-lobulated branched Reniei'a^ but none in its 
dermal layer nor in the surface-layer of the great tubular vents, found that 
they belonged to “ minute parasitical polypes, seated in dilated cavities, 
apparently of the excretory canals, the head of each polype averaging 100th 
of an inch in diameter, and supported on a short neck, which ended in a 
little saccular prolongation that was sunk into the sponge, and charged in its 
walls and tentacles with thread-cells so numerous that they appeared to ex- 
ceed in bulk the rest of the polype.” lie never found thread-cells in sponges 
without also discovering the parasitical polype from which they originated. 
Strange as is Elmer’s presumed series of nearly allied siliceous sponges 
exhibiting the various stages of evolution of the only organ considered 
distinctive between sponges and the Ccdentcrata, they yield in interest to 
his continued investigations of marine sponges, demonstrating an almost 
regular passage between these and the Hy droids, just as the phylogenetic 
theory would require it, and of which a short abstract is given in Verb. 
Ges. "Wiirz. iii. pp. xiii-xvi). In an Esperia, in another siliceous sponge 
allied to Myxilla^ and in a horny sponge the surface is studded with 
