500 Dr. W. B. Carpenter, [March 12, 



extemporizes, as it were, a stomach for itself in the substance of its 

 body, into which it ingests the solid particles that constitute its 

 food, and within which it subjects them to a regular process of diges- 

 tion. Hence these simplest members of the two kingdoms, which 

 can scarcely be distinguished from each other by any structural 

 characters, seem to be physiologically separable by the mode in 

 which they perform those actions wherein their life most essentially 

 consists. 



There are found, both in fresli and salt waters, numerous 

 examples of this Rhizopod type, which do not present any essential 

 advance upon the Amoeba and Actinophrys ; and a large proportion 

 of these are endowed with a shelly investment which may be either 

 calcareous or siliceous, — the former being the characteristic of the 

 Foraminifera, the latter of the Polycystina. In some of these tes- 

 taceous forms, the pseudopodia are put forth only from the mouth 

 of the shell, whilst in other cases this is perforated with minute 

 apertures for their passage ; but where there are no such apertures, 

 the sarcode body not unfrequently extends itself over the entire 

 external surface of the shell, and may give off pseudopodia in every 

 direction. Generally speaking, the Foraminifera live attached to 

 sea-weeds, zoophytes, &c. ; but their pseudopodia have a very ex- 

 tensive range, and form a sort of animated spider's web, most won- 

 derfully 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 radiation 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 connection 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 body 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 in its form and in its chambered structure. There is, however, 

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

 chambered shells formed by cephalopod moUusks, 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 body, 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 

 variation that may present itself within the limits of one and the 



