43G SUMMARY OF CURRENT RESEARCnES RELATING TO 



Cyclostoma and Pomatias.* — Dr. II. Simroth gives a comparativo 

 (lescriptidn of the anatomy of tliese two Neurobranchs, deducing 

 therefrom tbo conclusion that " Ci/clostoma and Pomntias belong to 

 two quite distinct and widely 6ei)arated families, which have inde- 

 pendently become adapted to crawling on the earth." He notes imssim 

 that Pomatias is the only known snail that in crawling shows an 

 internal movement from the anterior to the posterior border within 

 the "sole." In other cases (where the " locomotory wave" starts 

 posteriorly) the mechanism is muscular, but in Pomatias the wave is 

 due to a current of blood swelling the organ. 



Development of the Viviparous Edible Oyster.! — In this essay, 

 the text being duplicated in Dutcli and Frencli, Dr. R. Horst brings 

 together most of the informatitni of value which has been acquired by 

 his predecessors and contemporaries, and also gives an account of his 

 own investigations, especially those which relate to the development 

 of the shell-gland and gastrula, which he had, however, first published 

 two years ago. 



The gastrula is the first to be invagiaated ; this is followed by 

 the invagination of the shell-gland on nearly the opposite side of the 

 blastula. The mouth is formed at the time of invagination of the 

 gastrula ; the anus is formed later, and is broken through at the end 

 of the gastrula pouch of eudoblast, which blends with the ectoblast, 

 which also becomes perforated where the two blend. The mantle 

 cavity is formed by the appearance of a space between the i)08terior 

 margins of the larval valves, lined with ectoblast (mantle), into which 

 the vent opens. The anterior adductor muscle degenerates after 

 fixation, when its function is assumed by the posterior adductor, 

 which developes after the former. The cephalic ganglion originates 

 fr<.m an ejiiblastic thickening situated in the centre of the trochal 

 disk or velum. The larval shell is homogeneous; but at the. hinge 

 there are two small teeth separated by an interval from each other. 



Dr. Horst's more recent investigations upon the early growth and 

 fixation of the fry or veliger stage of 0. edalis and its metamorpliosis 

 into the " spat " are of great and significant interest. Carrying out 

 more fully a suggestion made by Mr. J. A. Ryder in 1881, Dr. Horst 

 used a wooden frame, into which could be fixed a number of glass 

 slides. This frame, with its slides, some of which were coated with 

 hydraulic cement, was immersed for a period of seventy-two hours in 

 water where free-swimming oyster larvje were known to exist, at the 

 end of which time sjiat was found adhering to the slides, measuring 

 0*24 mm. in height. After fixation the permaueut shell is formed or 

 built up by the mantle beyond the margins of the valves of the fry, a 

 homogeneous membrane, subdivided internally into polygonal spaces 

 or areas, being first laid down by the mantle border. In these 

 prismatic areas of the periostracum calcification occurs by the deposit 

 of calcic carbonate, and the shell is thus moulded upon the mem- 

 branous matrix of conchioline. 



* Zool. Anzeig., viii. (1S8.5) pp. lG-9. 



t Tijdschr. Ned. Dierk. Verecn. Pupid., 1884, pp. 1-C3 (I pi.). Cf. Amer. 

 Natural!, xix. (I88.j; pp. 317-8. 



