ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 627 



/3. Grastropoda- 



Secretion of Sulphuric Acid by Marine Gastropods.* —Dr. E. 

 Semon has experimented on the chemical and mechanical characters 

 which protect many animals against the hunger of their neighbours, 

 and has directed his attention especially to the abundant presence of 

 spicules. In this connection he was led to observe how various 

 " specialist " gastropods, e. g. Dulium galea, Tritonium nodiferum, and 

 Apli/sia, devoured Echinoderms in spite of their calcareous deposits. 

 Now these and many other marine gastropods have for long been known 

 to exude a fluid rich in free sulphuric acid. The possible uses of this 

 secretion are discussed, and the author concludes from his observations 

 that it plays a preliminary j)art in digestion, changing the carbonate in 

 the favourite food into readily pulverized sulphate of lime, and thereby 

 removing the obstacles in the way of such diet. 



Purple of Purpura lapillus.t — M. A. Letellier finds that the purple- 

 forming band in Purpura lapiUus is made up of a secreting epithelium 

 formed of ciliated cells, some of which are alone purj)urigenous, while 

 most merely produce mucus. The purple material is produced by three 

 substances, one of which is yellow and non-photogenic, while the two 

 others become blue and carmine-red under the influence of the rays of 

 the sun. After giving a careful chemical and crystallographic account, 

 the author expresses his opinion that the purple is produced by a true 

 chemical reduction. The function of this body, which is most abundant 

 during the breeding season, is comparable to the castoreum of Castor, 

 as it seems to bring about the congress of individuals for the purposes of 

 reproduction. 



Nudibranchiata of Liverpool District.^ — Prof. W. A. Herdman and 

 Mr. J. A. Clubb have a second report on the Nudibranchiata of the 

 Liverpool Marine District. Dendronotus arhorescens was found to vary 

 considerably in abundance at different periods of the year. The authors 

 have carefully studied its anatomy, and are able to add to or correct the 

 statements of Alder and Hancock and of Bergh. They did not find any 

 trace of prolongations from the liver extending actually into the rhino- 

 phores and the dorsal papillae ; the correction of the error is due to the 

 use of thin serial sections. In the sections of the cerata themselves 

 they find large spaces in the mesoderm containing blood-corj)uscles ; 

 these run, in the main, longitudinally ; they occasionally branch, and 

 they open into innumerable minute lacunas in the mesodermal tissues, all 

 of which here and there contain blood-corpuscles. There is a good deal 

 of pigmented connective tissue and ramifying threads of a brownish 

 colour ; these frequently give rise, in a surface view, to the appearance of 

 a dark-coloured granular central cascum, such as that figured by Bergh. 

 There are also to be seen masses of large distinctly nucleated cells lying 

 in meshes of fibrous connective tissue ; these are possibly mucus-secreting 

 glands, and occur chiefly in the smaller branches of the cerata. 



The upper end of each dorsal papilla of Eolis is occupied by a sac 

 containing a large number of thread-cells : this sac is evidently an 

 invagination of the ectoderm, and it communicates with the extei'ior by 

 a small but perfectly distinct and clearly bounded aperture at its apex, 



* Biol. Centralbl, ix. (1889) pp. 80-93. 



t Coniptes Rendus, cix. (1889) pp. 82-5. 



i Proc. Biol. Soc. Liverpool, iii. (1889) pp. 225-36 (1 pi.). 



