ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 769 



degree to the growth-type, for the structural material plays an 

 important part in determining the mode of growth of the Rhizopod 

 shell. 



Some of the Thalamophora construct their shells of aggliitiuated 

 foreign bodies, partly of inorganic (sand, mud), and partly of organic 

 nature, while the greater part of the Tbalamophoran shells are formed 

 by secretion of carbonate of lime ; the skeletons of the Radiolaria 

 consist of silica. As the two first constituents are far less firm than 

 silica, there is a corresponding difference in the habit and mode of con- 

 struction of the two great primary groujis of the Rhizopoda. Even a 

 slight examination shows that the shells of the Thalamophora are fur 

 stouter and more massive than the Radiolarian skeletons, which are 

 often exceedingly complicated, graceful, and elegant. The compara- 

 tively soft material which is employed by the former does not permit 

 them safely to erect such airy and complicated structures as the skeletons 

 of the latter, which are composed of solid, more or less elastic, 

 siliceous rods. 



The distinctions, however, are still more profound, and affect the 

 whole structural plan of the shells and skeletons. In the Radiolaria 

 both growth-types ajipear widely distributed, but there is an unmis- 

 takable preponderance of the concentric growth, while in the 

 Thalamophora the terminal growth-type is exclusively represented. 

 The cause of this difference is to be found in the fact that these two 

 modes of construction make different demands upon the solidity of the 

 material ; it is in the essence of the perforate-concentric mode of con- 

 struction that it requires to be carried out more lightly. As there is no 

 l^riucipal orifice the passage of the sarcode is by the jjores of the shell, 

 which must not be too narrow, nor the intervening skeletal jjarts too 

 massive ; further, the union of the latticed spheres concentrically nested 

 one within the other is only possible by means of free radial rods, 

 which, again, must not exceed a certain thickness. The conditions of 

 the pylomatic-terminal mode of construction are, obviously, very 

 different. 



The author quotes with approval the recent speculations of Neumayr, 

 as he proposes a phylogeny which agrees better with both the morpho- 

 logical and palfeontological facts than is the case with the older systems. 



In conclusion, attention is drawn to tlie interesting and significant 

 fact that Molluscan and Tbalamophoran shells follow the same laws of 

 circumvolution. This form must have its cause, not in the nature of the 

 organisms, but in the circumstances of the external world, and is 

 dependent on statical and mechanical requirements. 



RMzopod-Fauna of Bay of Kiel.* — Dr. K. Mobius, who has already 

 described the Infusoria of the Bay of Kiel,t now gives an account of the 

 Rhizopoda ; of the latter twenty-five species are now known, and as 

 sixty-three Infusoria have been described, it is clear that there are more 

 than eighty-eight Protozoa in this bay. In Actinolopus pedunculatiis, as 

 F. E. Schulze observed, the nucleus is near the top of the more acute 

 jjole of the oviform body. Vampi/rella pallida sp. n. is provided with 

 pseudopodia which have the i)ower of moving from side to side iu 

 pendulum-fashion ; it lives chiefly on the small diatom Navicula elliptica ; 



* Phys. Abhandl. K. Akad. Wiss. Bcrliu, ISSS (1SS9) Abb. ii., 31 pp., 5 pis. 



t Ante, p. 23 i. 



1889. 3 H 



