196 Miscellaneous. 



the membrane that lines the interior of the test ; of this it seems 

 to be only an expansion, and presents the same structure (epithe- 

 lium without connective tissue). 



The nervous ring has no relation with a supposed inferior vascu- 

 lar circle of the lantern. On its upper surface it presents a furrow 

 which divides it incompletely into two concentric bauds : the outer 

 of these passes entirely into the ambulacral cords ; the inner one 

 takes only an insignificant part in this formation. 



The ambulacral nervous cords, after having traversed the inner 

 surface of the ambulacral zones and become gradually thinner, 

 penetrate, in company with the ambulacral vessel, into the canal of 

 the ocellar plate, and terminate there against the portion of the 

 external integument which outwardly closes this canal. This ner- 

 vous termination presents no traces of a crystalline lens, or of any 

 optical apparatus justifying the retention for it of the name of eye 

 given to it by Valentin and Porbes. I have not succeeded in 

 demonstrating in it the least sensibility to light, whether artificial or 

 solar, and concentrated by means of a lens. The spot of pigment 

 described here is a pure fiction ; in this respect the so-called oculi- 

 form points do not enjoy any privilege. 



A series of branches spring, as is well known, at right angles 

 from each side of the ambulacral trunk. Each of them issues by 

 an ambulacral pore, penetrates into the ambulacral tentacle, tra- 

 verses its length, and terminates beneath the sucking-disk at a pad 

 serving as an organ of touch. 



Histology. — There is no reason for establishing a division into 

 ganglia and nerves in the nervous ring and the great trunks which 

 start from it ; all these parts have identically the same structure, 

 and must be regarded as nervous centres. 



Their brown coloration is due, not to scattered granules, as has 

 hitherto been supposed, but especially to the presence of large irre- 

 gular elongated cells (resembling the pigment-cells of the Batrachia) 

 filled with brown birefringent bundles : the nucleus is very appa- 

 rent ; for its neighbourhood is destitute of pigment. I regard these 

 cells as connective, seeing that I find them in other organs, espe- 

 cially in the walls of the aquiferous system, the membrane of the 

 lantern, &c. The nervous elements proper have already been 

 described by Baudelot and C. K. Hoffmann. They are fibrillae of 

 extreme tenuity and small bipolar cells. I have found that these 

 fibres and cells form two very distinct layers. The inner layer 

 presents only fibres ; the outer layer (that which is turned towards 

 the test) has a granular appearance. Examined under a high power 

 it shows an immense number of very small cells, only measuring a 

 few thousandths of a millimetre. These cells are so pressed against 

 each other that at the first glance we seem to have to do with an 

 epithelium ; but on examining them with more attention, and espe- 

 cially by exerting a slight pressure on the tissue while still fresh, 

 the cells separate from each other, and each of them shows two 

 very thin prolongations, which, at a certain distance from the cells, 

 present absolutely the aspect of the fibrillae of the inner layer. The 



