ENTOZOA. 63 



Usually only two individuals were seen to be attached to one another. 

 " Auch sah ich gewohnlieh nur zwei individuen aneinander kleben.* 



Dufour had conjectured, that the genus Gregarina might belong 

 to the Trematoda. Siebold, with better judgment, refers the genus 

 to the order Cystica. He describes several species ; and figures 

 some in the state of either conjugation or of spontaneous transverse 

 fission ; he describes this as two complete individuals sticking toge- 

 ther. Each shows the central multinucleate cell. Schleiden f has 

 viewed these Gregarinag as essentially a single organic cell, and 

 would refer them to the lowest group of plants. And here, indeed, 

 we have a good instance of the essential unity of the organic division 

 of matter. It is only the power of self-contraction of tissue, and its 

 solubility in acetic acid, which turn the scale in favour of the ani- 

 raality of the Gregarinae; they have no mouth and no stomach, which 

 have commonly been deemed the most constant organic characteristics 

 of an animal. 



Henle J and others have questioned the title of the Gregarina to 

 be regarded as an organic species or individual at all, or as any 

 thing more than a monstrous cell : thus applying to it my idea 

 propounded in 1843 of the true nature of the acephalocyst. 



In 1848 Kolliker§ published an elaborate memoir on the genus, 

 in which good and sufficient grounds are given for concluding 

 that the Gregarina not merely resembles, but actually is an ani- 

 mated being ; it stands on the lowest step of the animal series, 

 parallel with that of the single-celled species of the vegetable king- 

 dom. The Gregarina consists, as Schleiden and others have well 

 shown, of a cell-membrane, of the fluid and granular contents of the 

 cell, and of the nucleus with (occasional) nucleoli. The nucleus is 

 the hardest part, resisting pressure longest, like that of the Polygas- 

 trian. It divides, and its division is followed by spontaneous fis- 

 sion. Sometimes the establishment of the two centres of assimila- 

 tive force separates the cell-contents into two groups, without the 

 concomitant division of the cell-wall ; but an inner partition-wall is 

 developed. Stein believes that this is the result of the conjugation of 

 two individuals. However this may be, another mode of propagation 

 is then set up ; the granules of the divided cell-contents, as if im- 

 pregnated, develope cells, divide and subdivide, and are ultimately 

 resolved into embryos having the form of Navicellae ; but without the 

 siliceous shell. KoUiker is of opinion, from the frequent co-existence 

 of these pseudo-navicellar capsules with the ordinary Gregarinae and 

 the identity of structure of the capsules, prior to the development 



* LV. p. 57. t LVI. p. 97. X LVn.p.369. § VH. 



