ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 569 



Mollusca. 



Shells of Cephalopoda.* — Herr E. Eicfstalil, after pointing out the 

 different relations held to their shells by Cephalopoda and Gastropoda, 

 distinguishes the external shells of the Ammonites and recent Nautiloids 

 from the internal shells of Belemuites and Squids. The great differences 

 between shells depend on various modes of life ; those of the Ammonites 

 were almost more important as swimming organs than as defensive envelopes, 

 for they were generally very thin and light, much lighter than those of the 

 existing Nautilus ; the shells of Belemnites were very strong, and gave the 

 whole body great powers of resistance ; they were enclosed by a thick skin 

 rich in vessels, so that if they were injured they were rapidly healed. The 

 Sepi'de have a light shell, which is, however, fairly strong. With regard 

 to the formation of the septa, the author remarks that every septum arises 

 from its predecessor, becomes separated from it by the increase in length of 

 the intervening walls, and finally becomes a new strong septum ; in con- 

 sequence of this the hinder end of the body of the animal is always in 

 contact with a septum, and does not need to secrete either air or chalk. 

 There is good reason for ascribing to the Cephalopod-shell the independent 

 mode of growth which has been detected in the Lamellibranchiata, and 

 there is no reason for supposing that there is any secretion from the body 

 of the animal. 



Renal Organs of Prosobranchs-f — llerr G. Wolff gives a preliminary 

 notice of his observations on the renal organs of German Prosobranch 

 Mollusca, Paludina vivipara, Bithynia tentaculata, and Valvata piscinalis 

 having been examined. He has been able to convince himself of the 

 presence in all these of the internal orifice ; the great reduction which this 

 has suffered, greater even than in the Pulmonata, will explain Leydig's 

 failure to find it in Paludina ; it is least reduced in Valvata, where its 

 duct has long and strong cilia. In Paludina the pericardial opening of the 

 kidney is clearly in physiological connection with the opening of the kidney 

 into the water-reservoir, for the muscular fibres which inclose the former 

 are connected with the sphincter which embraces the latter. In Bithynia a 

 glandular body which corresponds to the kidney of Paludina projects freely 

 into the organ which may be regarded as the water-reservoir ; it differs 

 from Paludina in having two orifices, one upper and one lower, which 

 lead to the exterior ; the pericardial orifice is quite close to the former of 

 these. 



Glands in Foot of Tethys fimbriata.J — Dr. J. H. List finds consider- 

 able differences in the presence of glands on the upper and lower sides of 

 the foot of Tethys Jimbriata ; on the former there ai-e unicellular mucous 

 glands, unicellular glands with specially fornaed fat-like contents, which 

 may possibly be phosphorescent organs, unicellular glands with special 

 contents, some of which are often arranged in a lamellar manner, and 

 similar glands which have coarsely granulated contents. Of the numerous 

 glands there are two kinds; in one the foi-m of the gland is flask-like, and 

 these are bounded by a distinct membrane and contain two different masses, 

 which are arranged as in the goblet-cells ; there is a filar mass arranged in 

 a meshwork, and an interfilar mass. The second form of unicellular 

 mucous glands are quite like goblet-cells, even if they are not, as the author 

 believes, epithelial elements. The glands, which may have a phosphorescent 



* Naturforscher, xx. (1887) pp. 153-4, from PulseontograpLica, xxsii. (1886). 



t Zool. Anzeig., x. (1887) p. 317. 



t Zeitaclir. f. Wiss. Zool., xlv. (1887) pp. 308-26 (1 pi.). 



1887. 2 p 



