452 RECORD OF CURRENT RESEARCHES RELATING TO 



histology of Sagartia parasitica, Adamsia diapJiana, AntJiea cereus, 

 A. cinerea, Actinoloha dianthus, and Tealia crassicornis. 



The oral disk and the tentacles : here three layers can be made out, 

 an external and an internal epithelial layer, with between them a 

 supporting layer which is better developed on the oral disk than in 

 the tentacles, and which consists of a transparent fibrous ground- 

 substance with cells embedded in it. When the outer layer or ecto- 

 derm is subjected to higher powers it again may be seen to be divi- 

 sible into three layers ; the outermost is the best developed, and is 

 made up of extremely long and fine epithelial cells ; between the 

 basal ends of these cells there appears a thin layer consisting chiefly 

 of a special and finely granular substance, and then there follows a 

 single layer of muscular fibres; these three layers are regarded as 

 epithelial, nervous, and muscular. 



To the three layers found by Heider in the epithelial, the 

 Hertwigs add a fourth ; so that beside stinging, glandular, and 

 ciliated cells, there are also others which are sensory ; the simplest 

 are the ciliated, and these are very abundant ; they are remarkable 

 for each carrying a number of cilia ; the sensory cells are very evenly 

 distributed, but are perhaps a little more abundant towards the tip of 

 the tentacles ; they are exceedingly fine and filamentous, and are only 

 continued into a single process. The processes of the integument 

 may be divided into three sets : there are long delicate cilia, which are 

 chiefly connected with the ciliated cells and are distributed over the 

 whole surface ; the cnidocils (Heider) are small cones truncated at the 

 free end and seen, when examined with high powers, to be longitudi- 

 nally striated ; these stri« may further be broken up into a number 

 of separate cilia. The third set of processes consists of long filaments, 

 found only -on the tentacles, which appear to represent tactile pro- 

 cesses, and they are, in fine, cilia modified for a special purpose. 



In the nervous layer we find that cells of a special character are 

 associated with the fibres ; these are often of a considerable size, either 

 hemispherical or si)indle-shaped protoplasmic bodies with a large round 

 nucleus or nucleolus, and occupy a distinctly sub-epithelial position. 

 When this layer is successfully macerated, it is possible to draw out 

 the axis of the tentacle from its epithelial investment ; when the ecto- 

 dermal lamelltB are teased up it is often possible to find the nervous 

 layer remaining attached to a small piece, and so to get a nearer view 

 of the ganglion cells. These are best seen in the oral disk, where 

 the fine granules are found surrounding the large nucleus, and the 

 processes from the body, often of some size and length, become evi- 

 dent. The layer of nerve-fibres is seen to consist of a very thick and 

 regulai'ly well-developed network of fibrillte, which cross one another 

 at various angles and leave only small interspaces for the supporting 

 cells. The ganglion cells connected with it are bi-, tri-, or multipolar ; 

 the first-named are the rarest ; varying in size, they have the form of an 

 elongated spindle, and are continued at one end into a nerve fibrilla ; 

 The trijxjlar cells are more common, and generally give off three 

 fibrillcB, the multipolar are the largest and the most common ; they 

 often pass by a blunt process into the epithelial layer, and seem to be 



