ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 437 



• Attacliment and growth of the young edible oyster, according to 

 Horst, is very similar to that of the American species, as described 

 by Mr. J. A. Eyder.* The outgrowth of the first branchiae as two 

 series of distinct ciliated processes projecting into the mantle cavity 

 of the spat is interesting, as showing that the more primitive condi- 

 tion of the lamellibranchiate gill was much simpler than in the 

 existing adult oyster. 



Reproduction of Mytilus edulis-f — Prof. W. C. M'Intosh describes 

 the reproduction of the mussel {Mytilus edulis). The sexes are distinct 

 in the adult form, but in the undeveloped condition the structure of 

 the organs seems to be similar in both sexes. The shape of the valves 

 gives no reliable distinction. The reproductive elements are de- 

 veloped in the mantle : the male presents in January, in the thickened 

 generative region of the mantle, large pale round sperm-sacs filled 

 with minute spermatozoa, which have minute ovoid bodies with finely 

 filamentous tails. They are lively and tenacious of life. Twenty- 

 four hours' exposure, however, teems to be fatal to them. The 

 females have the same region of the mantle crowded with a pro- 

 digious number of minute ova. Throughout February the develop- 

 ment increases and the whole surface of the mantle becomes speckled 

 in both sexes with the reproductive elements. After full maturity is 

 attained, as in April, the orange mantle is richly marked in an arbo- 

 rescent manner by racemose sperm-sacs and ducts, esj^ecially towards 

 the margin. In the female this is not so evident, the ova being 

 grouped in masses and densely packed. 



i From this time the activity of the spermatozoa and the number of 

 the ova diminish, till in July neither ova nor spermatozoa can be 

 distinguished microscopically. 



Movement of the Foot in Lamellibranclis.l — Herr A. Fleisch- 

 mann contributes a short addition to the important question whether 

 mussels take in water into the blood system to assist in the move- 

 ments of the foot. The pores described by Griesbach are asserted to 

 have no existence, and the real cause of the dilatation of the foot is 

 to be sought for in the blood itself, which while the animal is at rest 

 is contained in reservoirs in the mantle ; when the foot is extended 

 the beat of the heart is accelerated and the blood is rapidly pumped 

 into the foot ; its reflux into the kidney is hindered by the closure of 

 valves. 



MoUuscoida. 



a. Tunicata. 



Development of Amaroeeium proliferiim.§ — MM. Ch. Maurice 

 and Schulgin find that the embryonic development of Amarcecium 

 proliferum much more resembles that of buds, as described by 

 Kowalevsky, than the ordinary development of embryos. Just as in 



* Bull. U.S. Fish Commission, ii. (1882) p. 383. 



t Ann. and Mag. Nat. Hist., xv. (1885) pp. 148-52 (2 figs.). 



X Zool. Aiizeig., viii. (1885) pp. 193-5. 



§ Aun. Sci. Nat.— Zool., xvii. (1884) 46 pp. (2 pis.). 



