ENTOZOA. 63 



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

 " Audi sah ich gewohnlich 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 Gregarinae 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- 

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

 have commonly been deemed the most constant organic characteristics 

 of an animal. 



Henle \ 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. Kolliker 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. % LVILp.369. § VII. 



