ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 563 



see that the mantle is in both rudimentary, and has become unable to 

 secrete a shell sufficiently large to form a protection for a whorl of 

 viscera. In the slug, the mantle retains its dorsal position, and is at 

 about the middle of the axis of the body ; in Testacella it is terminal 

 and ventral. In the slug the viscera pass into the foot, in Testacella 

 into the neck ; but in both the distribution of the nerves enables us to 

 establish the true nature of the parts which have been modified to the 

 purpose of new functions, and which have become irrecognizable. In con- 

 clusion Prof. M. Lacaze-Duthiers urges that, if modifications in the 

 position of some organs can change the general physiognomy and external 

 appearance of an animal, it is no less true that we ought not to regard 

 their displacement as affording a criterion of the highest value for the 

 characterization of classificatory divisions. Although the heart and lung 

 are altered in relation to the whole, they are not altered in their relation 

 to one another ; the heart is always intercalated between the body which 

 it has to nourish, and the lung from which it draws its freshened blood. 

 In so natural a group as the Pulmonata it is sometimes behind, sometimes 

 beside, sometimes in front of the lung, but its absolute position does not 

 alter. The corollary from this is that classifications based on the rela- 

 tive situation of lungs and heart ought to be revised. 



Absorption of Water.* — Herr A. rieischmann returns to the old 

 question of the taking in of water by molluscs. The affirmative position 

 maintained by Delle Chiaje was supported by the observations of KoU- 

 mann and Griesbach ; criticism has, however, weakened the latter, but the 

 recent researches of Schiemenz j seem to settle the question definitely. 

 To the latter and to his own investigations the author refers. 



Schiemenz has described with great definiteness the water-pores found 

 on the foot of Natica josephina. They are minute (7-8 /x in maximum 

 diameter), below them strong closing muscles are aggregated, from them 

 minute cavities extend into the foot. As to the physiology, Schiemenz 

 sets aside any mixture of water and blood, declares the vascular system 

 of Natica to be closed ; the elements of the foot (muscles, nerves, glan- 

 dular cells) are all inclosed and protected from the water by a limiting 

 membrane which surrounds vascular lacuna. The membrane also ex- 

 tends below the epithelium, and gives off protrusions including blood- 

 sinuses between the epithelial cells. 



The water is taken in as follows : — the vessels of the foot are richly 

 filled with blood ; the muscles become tense ; cavities are left between 

 them, and into these the water enters. When a sufficient quantity has 

 passed in, the closing muscles shut the pores, the animal moves with its 

 tense foot. 



Schiemenz has also noted, in another case, the modifications produced 

 in the blood by the introduction of water, and concludes that where the 

 vascular system and the histological system are not inclosed, there can 

 be no entrance of water. 



With the results reached by Schiemenz, Fleischmann entirely agrees. 

 He refers to the researches of Eoule and Grobben, which go against the 

 existence of pores, and believes that in most cases the blood and the 

 vascular sphincters are of themselves sufficient to explain the erection of 

 the foot. He maintains as before, in spite of Eoule's denial, the certain 

 existence of the "Keber venous valves." 



* Biol. Centralbl., vii. (1888) pp. 713-7. 



t MT. Zool. Stat. Neapel, vii. (1888) pp. 423-72. 



