420 



to suggest that certain minute spherical masses of sarcode, with 

 which some of the cells are filled, may be gemmules ; and that other 

 bodies, enclosed in firm envelopes, which he has more rarely met 

 with, but which seem to break their way out of the superficial cells, 

 may be ova. But on this part of the inquiry, nothing save observa- 

 tion of the animals in their living state can give satisfactory results. 



The regular type of structure just described is subject to nume- 

 rous variations, into a minute description of which the author next 

 enters ; the general results being, that neither the shape nor dimen- 

 sions of the entire disk, the size of the nucleus or of the cells form- 

 ing the concentric zones, the surface-markings indicating the shape 

 of the superficial cells, nor the early mode of growth (which, though 

 typically cyclical, sometimes approximates to a spiral), can serve as 

 distinctive characters of species ; since, whilst they are all found to 

 present most remarkable differences, these differences, being strictly 

 gradational, can only be considered as distinguishing individuals. 

 It thus follows that a very wide range of variation exists in this 

 type ; so that numerous forms which would be unhesitatingly 

 accounted specifically different, if only the most divergent examples 

 were brought into comparison, are found, by the discovery of those 

 intermediate links which a large collection can alone supply, to be- 

 long to one and the same specific type. 



After noticing some curious monstrosities, resulting from an un- 

 usual outgrowth of the central nucleus, the author proceeds to in- 

 quire into the essential character of the Orbitolite, and its relations 

 to other types of structure. He places it among the very lowest 

 forms of Foraminifera ; and considers that it approximates closely 

 to sponges, some of which have skeletons not very unlike the cal- 

 careous net- work which intervenes betv\>een its fleshy segments. Of 

 the species which the genus has been reputed to include, he states 

 that a large proportion really belong to the genus Orbitoides, whilst 

 others are but varieties of the ordinary type. This last is the light 

 in which he would regard the Orbitolites complanata of the Paris 

 basin ; which differs from the fully-developed Orbitolite of the 

 Australian coast in some very peculiar features (marking a less com- 

 plete evolution), which are occasionally met with among recent 

 forms, and which are sometimes distinctly transitional towards the 

 perfect type. 



