MICROSCOPIC FORMS OF ANIMAL LIFE. 21 



is generally clear, transparent, and structureless; but sometimes shows 

 radiating striae. When viewed sideways or obliquely, however, the ' cyatho- 

 liths ' are found to have a form somewhat resembling that of a shirt-stud 

 (figs. 1, 2, 7). Each consists of a lower plate, shaped like a deep saucer 

 or watch-glass; of a smaller upper plate, which is sometimes flat, some- 

 times more or less concavo-convex; of the oval, thick-wall, flattened cor- 

 puscle, which connects these two plates together at their centres; and of 

 an intermediate granular substance, which more or less completely fills 

 up the interval between the two plates. The length of these cyatholiths 

 ranges from about l-1600th to l-8000th of an inch, those of l-3000th of an 

 inch and under being always circular. It appears from the action of 

 dilute acids upon the Coccoliths, that they must mainly consist of calcareous 

 matter, as they readily dissolve, leaving scarcely a trace behind. When 

 the cyatholiths are treated with very weak acetic acid, the central corpuscle 

 rapidly loses its strongly refracting character; and there remains an ex- 

 tremely delicate, finely-granular membranous framework. When treated 

 with iodine, they are stained, but not very strongly; the intermediate sub- 

 stance being the most affected. Both discoliths and cyatholiths are com- 

 pletely destroyed by strong hot solutions of caustic potass or soda. The 

 Coccospheres (Fig. 3) are made up by the aggregation of bodies resembling 

 ' cyatholiths ' of the largest size in all but the absence of the granular 

 zone; they sometimes attain a diameter of l-760th of an inch. What is 

 their relation to the Coccoliths, and under what conditions these bodies 

 are formed, are questions whereon no positive judgment can be at pres- 

 ent given. (See 710.) 



GrREGARI^IDA. 



410. A very curious animal parasite is often to be met with in the 

 intestinal canal of Earthworms, Insects, etc., and sometimes in that of 

 higher animals, the simplicity of whose structure requires that it should 

 be ranked among the Protozoa. Each individual Gregarina (Fig. 294, A) 

 essentially consists of a large single cell, usually more or less ovate in form, 

 and sometimes attaining the extraordinary length of two-thirds of an 

 inch. 1 A sort of beak or proboscis frequently projects from one extrem- 

 ity; and in some instances this is furnished with a circular row of hook- 

 lets, closely resembling that which is seen on the head of Taenia. There 

 is here a much more complete differentiation between the cell-membrane 

 and its contents, than exists either in Actinoplirys or in Amceba; and in 

 this respect we must look upon Gregarina as representing a decided ad- 

 vance in organization. Being nourished upon the juices already prepared 

 for it by the digestive operations of the animal which it infests, it has no 

 need of any such apparatus for the introduction of solid particles into 

 the interior of its body, as is provided in the < pseudopodia' of the Ehizo- 

 pods and in the oral cilia of the Infusoria. Within the cavity of the cell, 

 whose contents are usually milk-white and minutely granular, there is 

 generally seen a pellucid nucleus; and when, as often happens, the cell 

 undergoes duplicative subdivision, the process commences in a constric- 

 tion and cleavage of this nucleus. The membrane and its contents, 

 except the nucleus, are soluble in acetic acid. Cilia have been detected 

 both upon the outer and the inner surface; but these would seem destined, 

 not so much to give motion to the body, as to renew the stratum of fluid 



1 See Prof. Ed. VanBeneden on Gregarina gigantia, in " Quart. Journ. Microsc 

 Sci.," N. S., Vol. x. (1870), p. 51, and Vol. xi., p. 242. 



