232 SUMMARY OF CURRENT RESEARCHES RELATING TO 



arc unipolar, and arc connected with tho ring by their processes. Tho 

 tentacular nerve-ring gives off a ncrvo for each tentacle, and these, at 

 the tips, aro broken up into a tuft of fibrils. Tho epithelium of the tips 

 appears to consist only of long fibrillar cells, with which it is probable 

 that tho separate nerve-fibres are connected. Four more interesting and 

 important nerves go to tho hinder end of tho proboscis, then bend round 

 the hinder end of the bulbus musculosus, and pass forwards towards the 

 oesophageal ring. Below the oesophageal opithclium these four nerves 

 form a kind of plexus, from which a number of small nerves are given 

 off. Between the epithelial cells there aro a number of ganglionic cells 

 which aro often seen to be in direct communication witli tho nerve- 

 trunks ; and tho epithelial cells themselves, which aro very elongated 

 and provided with long nuclei, aro connected by long processes with the 

 fibrils given off from tho nervous branches; this epithelium may bo 

 supposed to have a gustatory function. The author's account of tho 

 peripheral nervous systom is, unfortunately, in the form of a description 

 of his figures, and without them is unintelligible. 



The nervous system is invested in an outer firmer sheath — the outer 

 neurilemma or perineurium, and an inner supporting substance or 

 internal neurilemma. The general discussion of tho histological cha- 

 racters of the central nervous system of animals is a partial statement 

 of the views in the author's fuller essay (for which seo above). 



Echinodermata. 



Development of Antedon rosacea.* — Mr. II. Bury has investigated 

 the early stages in the development of Antedon rosacea. 



(1) External Form. The segmentation is regular, the gastrula by 

 invagination, the blastopore closes early, ciliation is at first uniform, but 

 differentiates into anterior tuft and five ciliated bands, the anterior band 

 is incomplete ventrally. There are two ciliated ventral depressions — the 

 " preoral pit " and the " larval mouth." The yellow cells appear before 

 the rupture of the vitelline membrane. Tho free larva swims with ter- 

 minal tuft forwards. A white patch on the left between the third and 

 fourth bands marks the position of the " water-pore." 



(2) Internal Anatomy. A mesoderm is budded off from the archen- 

 teron. The blastopore closes near the posterior end. The archenteron, 

 occupying the posterior half of the larva, divides into posterior dumb- 

 bell-shaped enterocoele, round the constricted part of which the anterior 

 half (mesenteron) grows to form a complete ring. The two swellings 

 of the dumbbell form the right and left body-cavities. The anterior 

 part of the mesenteron buds off the (left and ventral) hydrocoele and an 

 unpaired anterior body-cavity. The left body-cavity becomes anterior 

 and dorsal, the latter sends a five-chambered prolongation into the preoral 

 lobe to form rudiment of " chambered organ." The hydrocoele forms a 

 ring, incomplete to the left, on ventral side of mesenteron, and forms 

 five ventral pouches. Just before fixing, the anterior body-cavity opens 

 at water-pore. Fine lateral nerve-fibres below anterior tuft, preoral pit, 

 and down the sides of larval mouth disappear with loss of freedom. 



(3) Fixing. After twenty-four hours' swimming the larva fixes by 

 preoral pit ; the bands disappear ; the mouth invaginates to form vesti- 

 bule, which, as Barrois describes, is rotated to posterior end. Histolysis 



* Proc. Roy. Soc, xliii. (1887) pp. 297-9. 



