POLVGASTR1CA. 



be a few years ago, when they were thought to be mere specks of 

 living gelly, imbibing nourishment at every point of their surface, 

 which became diffused through all parts of the homogeneous tex- 

 ture of their bodies, such a mode of multiplication would be per- 

 fectly intelligible, and every step of the process easily understood : 

 but setting aside the conformation of their digestive apparatus, 

 which, as we have before observed, is in our opinion not satisfac- 

 torily determined, there are many circumstances attending the 

 operation, which would indicate a power of developing new organs 

 in the construction of every fresh individual, which must be looked 

 upon as a very interesting feature in their history. Thus a new 

 oral orifice, surrounded with cilia, must be formed upon the poste- 

 rior segment of each divided animalcule, while an anal aperture is 

 developed upon the anterior half. In Nassula elegans (Jig. 17, 1) 

 the dental apparatus a, complex as its structure seems to be, must 

 be formed upon a new part of the body preparatory to every sepa- 

 ration ; and accordingly, in the plates which Ehrenberg gives of the 

 reproduction of this animalcule, a new mouth or dental cylinder is 

 actually seen to sprout from the hinder half of the creature before 

 its transverse fissure is complete. These structures therefore, and 

 others hereafter to be mentioned, must continually be called into 

 existence at new and distant parts of the system. 



(89.) We have as yet only spoken of those forms of fissiparous 

 generation in which the original animalcule divides either trans- 

 versely or longitudinally into two portions ; yet there are instances 

 where several new beings result from a like process. In Gonium 

 pectorale (Jig- 16, 6) the entire animalcule seems to consist of 

 sixteen globules enclosed in a delicate film or capsule ; which, 

 divides both in a transverse and longitudinal direction, so as to 

 separate into four portions, each composed of one large and three 

 smaller globules, which, after their separation from the rest, swim 

 freely about, and soon develope the parts and assume the appear- 

 ance of the parent. In Gonium pulvinatum the offspring is still 

 more numerous ; the parent resembles a square piece of delicate 

 membrane, and, on assuming its full growth, is seen to be marked 

 by three transverse and as many longitudinal lines, crossing each 

 other at right angles, and dividing the original into sixteen smaller 

 squares, which soon separate from each other, and become as many 

 detached beings. 



(90.) Productive as the above-mentioned modes of increase 

 are, it would seem that they are not the only sources of propagation 



