Dr. Carpenter on the Rhizopod Type of Animal Life. 77 



Generally speaking, the Foraminifera live attached to sea-weeds, 

 zoophytes, &c. ; but their pseudopodia have a very extensive rano-e, 

 and form a sort of animated sj)ider's-web, most wonderfully adapted 

 for the prehension of food. The absence of any membranous 

 investment to these threads is clearly indicated by their fusion or 

 coalescence when two or more happen to come into contact ; and 

 sometimes a fresh expansion of sarcode takes place at spots remote 

 from the body, so as to form new centres from which a fresh radi- 

 ation of pseudopodia proceeds. 



By far the greater number of Foraminifera are composite fabrics, 

 evolved, like zoophytes, by a process of continuous gemmation, each 

 gemma or bud remaining in connexion with that from which it was 

 put forth ; and according to the plan on which this gemmation 

 takes place, will be the configuration of the composite bodv thereby 

 produced. Where the segments succeed each other in a line, that 

 line is very commonly bent into a spiral ; and each new segment 

 being a little larger than the preceding, the spire gradually opens 

 out, so that the shell very closely resembles that of the Nautilus, 

 both m its form and in its chambered structure. There is, however, 

 this essential difference, — that whereas in the Nautilus and other 

 chambered cells formed by cephalopod mollusks, the animal lives 

 only in the outermost chamber, all the inner ones having been suc- 

 cessively vacated by it, each chamber in the foraminiferous shell 

 continues to be occupied by a segment of the composite bodv, com- 

 municating with the segments within and without by threads of 

 sarcode, which traverse minute* passages left in the partitions between 

 the chambers. In the classification of these forms, an extraordinary 

 amount of allowance has to be made for the very wide range of vari- 

 ation that may present itself within the limits of one and the same 

 specific type. It is very easy to select from any extensive collection 

 of Foraminifera, recent or fossil, sets of forms having certain characters 

 in common, but yet so dissimilar in other respects that few naturalists 

 would have any doubt as to their specific or even generic distinctness; 

 yet when the collection is thoroughly examined, such a series of 

 intermediate forms is found to exist, as connects all these by grada- 

 tions so insensible as to prevent the possibihty of any line of demar- 

 cation being satisfactorily drawn between them. A remarkable ex- 

 ample of this kind is presented by the generic types designated as 

 Dendritina and Peneroplis ; the former being a minute shell, re- 

 sembling that of the Nautilus in its general proportions, and having 

 a single large dendritic aperture in its successive partitions ; whilst 

 the latter is flattened, and instead of one large aperture, has a scries 

 of small foramina arranged in a single line. Now between these 

 every gradation can be found, both in the form of the shell and in 

 the mode of communication through the septa ; the flattened shell 

 of Penerop/is presenting various degrees of turgidity until it attains 

 the proportions of Dendritina ; and the linear arrangement of the 

 isolated apertures, in like manner, giving place to one in which they 

 are approximated more closely together into a sort of bundle, still, 

 however, retaining their distinctness ; whilst in other individuals. 



