172 PROCEEDINGS OF SOCIETIES. 



concentric zones of closed cells, and having minute pores at the 

 margin. Starting from the central nucleus, — which consists of a 

 pear-shaped mass of sarcode, nearly .surrounded by a larger mass 

 connected with it by a jjeduncle, — the development of the Orbitolite 

 may take place either on a simple, or upon a complex type. In the 

 former (which is indicated by the circular or oval form of the cells, 

 whicli show themselves at the surfaces of the disk, and by the single- 

 ness of the row of marginal pores), each zone consists of but a single 

 layer of segments, connected together by a single annular stolon of 

 sarcode; and tiie nucleus is connected with the first zone, and each 

 Zi)ne with that which surrounds it, by radiating peduncles proceeding 

 from this annulus, which, when issuing from the peripheral zone, will 

 pass outwards through the marginal pores, probably in the form of 

 pseudopodia. In the complex type, on the other hand (which is 

 indicated by the narrow and straight-sided form of the superficial 

 cells, and by the multiplication of the horizontal rows of marginal 

 pores), the segments of the concentric zones are elongated into 

 vertical columns with imperfect constrictions at intervals ; instead of 

 a single annular stolon, there are two, one at eitlier end of these 

 columns, between wliich, moreover, there are usually other lateral 

 communications ; whilst the radiating peduncles, which connect one 

 zone witli another, are also multiplied, so as to lie in several planes. 

 Moreover, between each annular stolon and the neighbouring sur- 

 face of the disk, there is a layer of superficial segments, distinct from 

 the vertical columns, but connected with the annular stolons ; these 

 occupy the narrow elongated cells just mentioned, which constitute 

 two superjicial layers in the disks of this type, between which is the 

 intermediate layer occupied by the columnar segments. 



These two types seem to be so completely dissimilar, that they 

 could scarcely have been supposed to belong to the same species ; 

 but the examination of a large number of specimens shows, that 

 although one is often developed to a considerable size upon the 

 simple type, whilst another commences even from the centre upon 

 the complex type, yet that many individuals which begin life, and 

 form an indefinite immber of annuli, upon the simple type, then take 

 on the more complex mode of development. 



The author then points out what may be gathered from observa- 

 tion and from deduction respecting the Nutrition and mode of 

 Growth of these creatures. He shows that the former is probably 

 accomplished, as in other Rhizopods, by the entanglement and draw- 

 ing in of minute vegetable particles, through ihe instrumentality of 

 the pseudopodia; and that the addition of new zones probably takes 

 place by the extension of the sarcode through the marginal pores, 

 so as to form a complete annulus, thickened at intervals into seg- 

 ments, and narrowed between these into connecting stolons, the 

 shell being probably produced by the calcification of their outer 

 portions. And this view he supports by the results of the examina- 

 tion of a number of s})ecimens, in which reparation of injuries has 

 taken place. Regarding the Reproduction of Orbitolites, he is only 

 able to suggest that certain miimte spherical masses of sarcode, with 

 which some of the cells are filled, may be gemmulcs ; and that olht-r 



