178 CURRENT LITERATURE. 



these plates or have them weakly represented, while those living on the shore 

 have them strongly developed, and often corrugated. He also believes sutural 

 tufts " to be the direct result of over-nutrition of the girdle at the sutures, caused 

 by its greater mobility at those points." An interesting seven-valved specimen of 

 Mopalia ciliata, Sow., is figured, in which there is no trace of the missing valve, 

 and there is no striking change in the general appearance of the animal. A little 

 more care might be used with the plates ; in one copy, plate 52 has had some 

 paper placed on it before it was dry, while plate 46 literally has a hole in it, and 

 other marks due to a wet plate having been laid on its back. — E. R. S. 



Tomlin, Brockton.— The Genus Rissoa (contd.). Brit. Nat., 1893, PP- I22_ 3- 



Kuster, H. C. — Systematisches Conchylien-Cabinet, fortgesetzt von Kobelt. 

 40 pp., 6 pits. Lief. 396. (Contains part of Cerithium). 



Woodward, B. B. — Recent Progress in Conchology. Nat. Sci., 1893, iii., 

 PP- 33-9- 



STRUCTURE AND DEVELOPMENT. 



Barrois, J. — Anat. dei Cryptazeca monodoiita. Rev. d. Sci. Nat. de l'Ouest, 

 Tom. ii, No. 3, pp. 3201. 



Collinge, Walter E. — The Morphology of the Generative System in the Genus 

 Testacella. Ann. & Mag. N. H., 1893, pp. 21-5, pi. 1. 



Fischer, H. — Sur quelques travaux recents relatifs a la Morphologic des 

 Mollusques univalves. Journ de Conchyl., 1893, pp. 5-15. 



Heymons, R.— Zur Entwicklungsgeschichte von Umbrella mediterranean Lam., 

 Zeit. f. wiss Zool., 1893, lvi., pp. 245-9S, pis. xiv. -xvi. 



Dr. Heymons gives a careful and clearly illustrated account of the develop- 

 ment of the egg of Umbrella up to the veliger stage. Segmentation is total, and 

 after two divisions (transverse and sagittal), the embryo consists of four macromeres 

 lying in one plane, exhibiiing an animal pole above and a vegetative pole below. 

 Three generations of micromeres are produced by successive equatorial divisions of 

 the four macromeres at their animal poles. The micromeres multiply and form 

 a cap of cells (primitive epiblast) over the dorsal side ( = animal pole) of the 

 embryo : this gradually extends over the ventral surface as well. The mesoblast 

 arises by separation of a cell from the left posterior macromere ; it then divides 

 into a right and left half, and these by sub-division give rise to two solid paired 

 mesoblastic bands lying one on each side of the hypoblast posteriorly. The 

 hypoblast is formed by further sub-division of the primilive macromeres. Gastru- 

 Iation is effected by a sinking inwards of the hypoblast at the vegetative ( = ventral) 

 pole, accompanied by epibolic growth of the epiblast up to the lips of the 

 blastopore so formed. The blastopore is at first elongated, wider in front than 

 behind, and extending from the middle to the posterior extremity of the embryo : 

 eventually it completely closes from behind forwards. Mouth and anus arise by 

 epiblastic involutions on the sites of the former extremities of the blastopore. 



The author discusses the significance of his results, which in many points 

 curiously resemble the developmental processes recently described by Wilson 

 in Nereis. The mesoblastic bands enclose no codomic cavities, such as Erlanger 

 has observed in several Gastropods: they are, nevertheless, of distinctly hypoblastic 

 origin. Heymons concludes his valuable paper with an account of the excretory 

 organs of the larva. 



Moss, W. ( and Paulden, F. — Reproductive organs of Bulimus acutus (Helix 

 acuta). Trans, and Ann. Rpt. Manchester Micro. Soc, 1892, pp. 75-9 ; 

 pi. ii. 



Simroth, H. — Some remarks with respect to Mr. Wotton's paper on the Life- 

 History of A. ater. Journ. Conch., 1893, pp. 208-9. 



