ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 497 



The study of a series of sections shows that the histological separation 

 of the centres is not more marked in the upper part of the nervous mass, 

 where authors seem to agree in recognizing the presence of pedal ganglia 

 and the first two asymmetrical ganglia, than in the lower part of the 

 nervous mass. The study of larvae shows that the ventral mass is 

 certainly formed of two distinct nerve-cent.res (first two asymmetrical 

 ganglia and pedal ganglia). If it is impossible to establish a histological 

 distinction between the two centres, on account of the continuity of the 

 layer of peripheral nerve-cells, it is quite easy to distinguish in the 

 nervous mass, by the aid of the groove and of the two orders of nerves, 

 what part belongs to either of the fused centres. An examination of 

 sections shows that the general form of the four ganglia which serve to 

 form the nervous mass as a whole, is that of four cylinders united by 

 pairs, and closely applied to one another by one of their faces. The 

 structure of the epipodium and the close relations which it has with the 

 mantle in the young Fissurella should lead us to regard it as part of the 

 mantle, and to keep for it the name of inferior mantle. 



Descent of Ova in Helix.* — M. J. Perez has investigated the descent 

 of the ova in the canal of the hermaphrodite gland of Helix. At what- 

 ever season the eff'erent canal is examined, the inferior part of the tube 

 is always found filled with sperm. It is evident that the ova must pass 

 through the efferent canal a short time before they are found in the 

 diverticulum. The author has dissected a large number of specimens 

 day by day. He found in some that the canal was less distended by 

 sperm than usual, and had a peculiar greyish appearance. Microscopic 

 examination of the contents showed that the sperm was more or less 

 completely altered, and that the epithelium of the efferent canal was also 

 being destroyed. When the sperm and epithelium are both completely 

 absorbed, the efferent canal is empty and the way is open for the ova. 

 The author has not yet been able to observe their passage directly, and 

 thinks it is effected in a very short time. 



Anatomy of Clione limacina.t — Herr P. Schalfejefi" commences by 

 directing attention to the so-called jaws of this mollusc. The w-alls of 

 the sheath are formed of a thick layer of circular muscles covered by a 

 very thin investment of connective tissue. When at rest the jaws have, 

 externally, a layer of longitudinal muscles, part of which forms the 

 retractor of the seizing apparatus ; the spaces between the muscles contain 

 connective substance which forms a thick layer of fibrous appearance, a 

 cylindrical epithelium, and an armature of hooks which is connected 

 with the epithelium. The hooks consist of a horny substance which is 

 not chitin, and rcbts on giant-cells, the finely granular protoplasm of 

 which fills up the hollow of the tooth, as far as its tip. Similar 

 characters have been observed in Pneumodermon. 



As to the connection between the organ of Bojanus and the pericardial 

 cavity, the author affirms that there is not merely an opening, but a 

 typical funnel ; the epithelium of this, which is characterized by very 

 long flagella, passes on the one side into the very flat ejjithelium which 

 covers the inner surface of the pericardial cavity, and on the other into 

 the glandular epithelium of the kidney. 



* Comptes Eendus, cviii. (18S9) pp. 3G5-7. 

 t Zool. Auzeig., xii. (1889) pp. 188-90. 



