95G SUMMARY OF CURRENT RESEARCHES RELATINQ TO 



layer whicli appears to be much less important. A protoplasmic tunic, 

 perforated only by tho ductus ejaculatorius, forms the innermost layer 

 of the body-wall ; it consists of an irregular layer of granular proto- 

 plasm, in which nuclei arc imbedded at frequent intervals, but which 

 does not show any trace of division into distinct cells. From its inner 

 wall numerous processes arc given oflf which anastomose witli ono 

 another in the cavity of the body, and so form a reticulum whicli is 

 continuous with or forms an investment for the remaining organs of tho 

 animal. A number of mucous glands which open to the exterior are 

 imbedded in the tunic. 



The brain is transversely elongated, and is imbedded in the tissue at 

 the anterior end of the body ; it is composed of a mass of fibres, below 

 which is a layer of nerve-cells ; a nerve of precisely the structure of tho 

 brain goes on each side for a short distance round the edge of tho 

 creature. 



The mouth is merely a small perforation of the ventral cuticle, round 

 which the muscles and other tissues do not seem to have undergone any 

 special modification ; the alimentary tract consists of a large mass of 

 protoplasm, continuous at the sides of the mouth with the general tunic ; 

 nuclei seem to be absent, except occasionally at the edge of the mass. 

 Vacuoles are frequently found, containing generally small crustaceans 

 in various stages of decomposition. It is possible that prey are captured 

 by the protrusion of pseudopodia from the mouth. 



There is a single testis and a pair of ovaries ; the former is a mass 

 of large, deeply staining cells, not separated by any definite investing 

 membrane from surrounding structures ; the spermatozoa do not appear 

 to have vibratile tails ; the scmiual vesicle is simply a space in the 

 general somatic reticulum, which is a little larger than usual. Tho 

 ductus ejaculatorius appears to be lined by a thick continuation of tho 

 ventral cuticle. The ovaries each contained less than twenty ova ; each 

 ovum is granular in young and spongy in older specimens ; the large 

 vesicular nucleus has a reticulum, which generally breaks up during tho 

 preparation of sections ; the nucleolus is a remarkable rounded structure 

 of considerable size ; the ova are, for a time at any rate, surrounded by 

 a delicate follicular epithelium ; no oviduct could be made out, and it is 

 suggested that the ova escape by the mouth. The author was unable to 

 form any ojiinion as to the presence or absence of an excretory system. 

 Neglecting it, the other characters of Haptodiscus seem to be exactly 

 such as might bo looked for in a free-living Cestode which had either 

 retained or acquired a mouth. On the other hand, it may be conceived 

 to be a Cestode (>r Trematode larva which had acquired reproductive 

 organs. 



Echinodermata. 



Anatomy of Echinothurida and Phylogeny of Echinodermata.* 

 Drs. P. and F. Sarasin have issued another part of their beautifully 

 illustrated account of their researches in Ceylon ; the description of tho 

 anatomy of the Echinothurida is chiefly based on their new species 

 Asthenosoma urens. The skeleton is first dealt with ; the ambulacral 

 primary plates do not fuse to form secondary plates. The oral area is 

 just like that of the Cidarida, being covered by five double rows of 

 imbricating plates, each of which is perforated by an ambulacral pedicle. 



* Ergebnisse Naturw. Forschungcn auf Ceylon, i. (1888) pp. 83-154 (8 pis.). 



