ZOOLOGY AND BOTANY, MIOKOSCOPY, ETC. 565 



said to resemble them in structure are the so-called eyes on the tentacles 

 of Gardium, and these are possibly luminous organs. 



All the available interstices of the mantle-margin of a Tridacna were 

 found to be densely packed with " green cells " or pseudochlorophyll 

 corpuscles. These, which are certainly true cells, have a distinct 

 nuclear framework, which is very deeply coloured by Grenacher's alum- 

 carmine. The nucleus is ordinarily spherical, but sometimes oblong or 

 reniform, and not unfrequently, especially in alcoholic preparations, 

 strikingly stellate. Increase by transverse division was also observed. 

 There is some reason for believing in the presence of a special (cellu- 

 lose ?) envelope. The green colouring matter is fixed by chromic acid, 

 but extracted by alcohol; it is not generally diffused through the 

 protoplasm, but localized in small round corpuscles, which are dis- 

 tributed through the cells in variable numbers. It was not possible to 

 decide definitely whether the corpuscles are situated in the vacuoles or 

 in the protoplasm, but more probably they lie in the latter. These 

 symbionts are not, as is generally the case, found in the cells of the 

 host, but float freely in the cavities of the system of blood-lacunae. 



The protoplasm of the blood-corpuscles was found to have distinctly 

 separated into two different constituents, a perfectly hyaline part, in 

 which the nucleus was always situated excentrically, and a " proto- 

 plasmatic " part which showed a very marked fibrous coagulation. This 

 was observed in all of those specimens which had been treated respec- 

 tively with chromic acid, alcohol, and osmium. In addition to the 

 ordinary amoeboid blood-cells, there were a few bodies which were very 

 characteristic of the blood ; these were rounded, or oval, lobate, or 

 otherwise irregularly formed cells, the protoplasm of which was so 

 completely filled with strongly refractive granules of a fatty nature that 

 no cell-nucleus could be found. These "granule-cells" usually attain 

 twice or three times the size of the ordinary blood-cell, and they often 

 lie close to the walls of the blood-lacunae, in recess-like depressions. 

 These cells have a very remarkable resemblance to certain cells of the 

 interstitial connective substance of the Pulmonata, which were first de- 

 scribed by Semper. It is probable that in both cases the cells have 

 some relation to glycogen, or a glycogen-like compound. 



With regard to the much discussed question as to intercellular spaces 

 in the epithelium of MoUusca, Herr Brock states that of his three 

 Tridacnse, the osmium and chromic acid specimens did not present the 

 smallest interstices between the individual cells, while the spirit 

 specimen had the whole epithelium traversed by numerous large typical 

 intercellular spaces. As only one of these can represent the natural 

 condition, the comparative value of the preservative fluids has to be 

 taken into consideration. The author declares against the spirit and 

 the spaces. 



Phylogeny of Lamellibranehs.* — Dr. B. Sharp submits some con- 

 siderations on the phylogenetic classification of Lamellibranehs. He 

 regards the entire group as degenerate, as derived from Gastropoda, and 

 as represented in primitive form by forms like Nucula and Trigonia. 

 The loss of one adductor is referred to mechanical causes. This is 

 followed through Mytilus and Pinna to Ostrea. A passage from regular 

 to irregular shell is to be seen in the fresh-water forms. Unio repre- 



* Proc. Acad. Nat. Sci. Philad., 1888, pp. 121-4. 

 1888. 2 n 



