ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 955 



of the epithelium, the so-called " protoplasmic processes " of the cells, 

 the distribution of cilia, the formation of the epicuticula, &c, Herr 

 Drost discusses somewhat minutely the relation of certain dark brown 

 spots at the upper end of both siphons. These turned out to be 

 bottle-like glands of pigmented cells, variously divided, and opening 

 by a minute efferent duct. Two other forms of glands occur. The 

 bottle-shaped mucous glands, described by Flemming in Mytilus, are 

 distributed all over the mantle margin, but in especial abundance 

 under the ciliated epithelium. A third form occurs on the mantle 

 margin and on the siphons on the external surface, but only in the 

 zone covered by the young epicuticula or the shell. All these types 

 are carefully described. -Below the epithelium a distinct hyaline 

 layer is everywhere demonstrable, of obvious importance as a basis 

 of attachment for the muscles. Below the epithelium in the siphons 

 there is a thin layer of fine circular muscles ; this is succeeded by a 

 very thin sheath of delicate longitudinal muscles. The separation 

 of the subepithelial from the others does not always occur. In the 

 cirri and in the mantle the connective tissue and radial muscles are 

 continuous with the epithelium. The greater portion of i the siphon 

 wall is formed of the main muscular masses, which consist of longi- 

 tudinal and circular fibres developed in variable proportion. But 

 besides these, other muscles connect the outer and inner surfaces of 

 the siphon wall, and lie at right angles to both the two systems 

 just mentioned. The latter occur isolated or in small bundles at 

 approximately regular intervals. The disposition of these three 

 systems in the mantle is then described. 



The memoir closes with a discussion of the controversy between 

 Flemming and Kollmann as to the nature of the connective tissue. 

 Herr Drost's results confirm Flemming's opinion. He maintains the 

 cellular nature of Langer's vesicles. The fibrous tissue near the optic 

 ganglion is finally discussed, and its probable derivation from 

 modified mucus-cells is maintained. 



Moiluscoida. 

 o. Tunicata. 



Structure of Amaraecium torquatum.* — M. C. Maurice has 

 studied the structure of the above-named compound Ascidian, and has 

 established a number of new facts in regard to the anatomy of such 

 forms. 



I. The branchial system. — The branchia consists of thirteen series 

 of stigmata, and exhibits three main peculiarities, (a) The trans- 

 verse sinuses which separate the stigmata are fused directly with the 

 internal tunic on each side of the endostyle, over about a third of their 

 circumference ; elsewhere numerous trabecule bind them to the tunic. 

 From this it follows that the peribranchial cavity is subdivided into 

 a series of secondary cavities, open towards the cloaca, and closed by 

 culs-de-sac towards the endostyle. (6) Along each of the transverse 

 sinuses, the branchial wall forms a continuous fold, hanging into the 



* Comptes Iteiulus, ciii. (1880) pp. 43t-6. 



