878 SPONGES AJND ZOOPHYTES 



pol vpites, as well as the soft flesh that connects together the members 

 of aggregate masses, are consolidated by calcareous deposit into stony 

 corals ; and the surfaces of these are beset with ' cells,' usually of a 

 nearly circular form, each having numerous vertical plates 01- lamella' 

 radiating from its centre towards its circumference, which are 

 formed by the consolidation of the lower portions of the radiating 

 partitions that divide the space intervening between the stomach and 

 the general integument of the animal into separate chambers. This 

 arrangement is seen on a large scale in the Fumjla, or ' mushroom- 

 coral ' of tropical seas, which is the stony base of a solitary anemone- 

 like animal ; on a far smaller scale, it is seen in the little Cavyo- 

 j/////llif(. a like solitary anemone of our own coasts, which is scarcely 

 distinguishable from an Actinia by any other character than the 

 presence of this disc, and also on the surface of many of those stony 

 corals known as ' madrepores ; ' whilst in some of these the indivi- 

 dual polype-cells are so small that the lamellated arrangement can 

 only be made out when they are considerably magnified. Portions 

 of the surface of such corals, or sections taken at a small depth, are 

 very beautiful objects for low powers, the former being viewed by 

 reflected and the latter by transmitted light. And thin sections of 

 various fossil corals of this group are very striking objects for the 

 lower powers of the oxy-hydrogeii microscope. An exceedingly use- 

 ful method of preparing sections of corals has been devised- by 1 )r. ( ! . 

 von Koch ; the corals with all their soft parts in plate are hardened 

 in absolute alcohol, and then placed in a solution of copal in chloro- 

 form. After thorough permeation they are taken out and dried 

 slowly until the masses become quite hard. These masses may now 

 be cut into sections with a fine saw and rubbed down tin a whetstone 

 in the ordinary manner ; after staining, the sections may be mounted 

 in Canada balsam. The great value of this method lies in the fact 

 that by it the soft and hard parts are retained in their proper rela- 

 tions with each other. 1 



The chief point of interest to the microscopist, however, in the 

 structure of these animals lies in the extraordinary abundance and 

 high development of those filiferous capsules.' or ' thread-cells,' the 

 presence of which on the tentacles of the hydroid polypes has been 

 already noticed, and which are also to be found, sometimes sparingly 

 sometimes very abundantly, in the tentacles surrounding the mouth 

 of the Medusa 1 , as well as on other parts of their bodies. If a 

 tentacle of any of the sea-anemones so abundant on our coasts (the 

 smaller and more transparent kinds being >eleded in preference) be 

 cut off, and be subjected to gentle pressure between the two glares 

 of the aquatic box or the compressorium. multitudes of little dart- 

 like organs will be seen to project themseh es from its surface near 

 its tip : and if the pressure be gradually augmented, many additional 

 darts will every moment come into view. Xot only do these organ> 

 present different forms in different species, but even in one and the 

 same individual very strongly marked diversities are shown, of 

 \\liich a few examples are given in fig. (500. At A, B, (.'. 1) is 

 shown the appearance of the ' filiferous capsules.' whilst as yet the 



1 Sec Zi'idloii/xc/irr Air:r/ffi /, i. p. :;<',; and I'm*-. Z*"},il. Sin-. London, Isso, p. -jj. 



