36 



LOWER INVERTEBRATES. 



secretes a lorica of the pristine beauty of its species, soon acquires a collar and flagellum, 

 and is henceforth indistinguishable from its mature kindred. In the 

 recently described Spongomonas haeckeli, we are made acquainted with 

 a most remarkable infusorian, — one which, if it fulfils the expectation 

 of the discoverer, Mr. Kent, will prove of unusual interest to a large 

 number of students in zoology, and its dedication to Prof. Haeckel 

 particularly apt. The zooids differ firom the preceding only in being 

 more plastic, the collar and flagellum being suddenly withdrawn on the 

 least disturbance, the body then taking on an amoeboid aspect. The 

 animals secrete a mucilaginous stratum in which they dwell, studding 

 its surface when expanded. Should this disposition of the zooids take 

 place in " sacular invaginations of this matrix, it would produce what 

 would have to be accepted as an undoubted, .though very rudimentar}-, 



in Codciga. SpOnge-StOck." 



Fig. 30.— Fission 



SuB-OeDEK VI. — EtrSTOMATA. 



The Eustomata differ from the forms previously described, inasmuch as they 

 have a definite oral aperture, instead of ingesting their food at any part of their sur- 

 face, or, as in the collared monads, only at a disc bordered by the collar ; they differ 

 also in having the outer part of their bodies much firmer than the endosarc, hence 

 they are as a rule less plastic, and in a few instances the outer layer is indurated after 

 the manner of some of the higher CiUata. They never have more than two flagella, so 

 they are separated into groups of families, according as the zooids have one or two 

 flagella. The forty-six genera are distributed among eleven families; there are in- 

 cluded many forms well-known to observers of pond-life. 



In the first family (Astasid^) the monads are free, constant in form, colorless, the 

 generic differences being found in the shape of the body, — ovate, flattened, flask-shaped, 

 etc. ; it includes Astasia with a distinct tubular pharynx, and Colpodella without it. 

 Astasia trichophora is frequently met with in marsh-water. Although its forms are 

 protean, perhaps its more usual attitude is pyriform ; from the narrower anterior end 

 issues a cord-like flagellum, mistaken by Ehrenberg for a neck like that of Trachelocera 

 olor (Fig. 39). The ingestive orifice "consists of a large, widely dilatable, but simple, 

 aperture, continued backwards into a clearly-defined pharyngeal tract." This structural 

 character marks a broad distinction between this genus and Euglena. Btitschli has 

 shown that the contractile vacuole of A. trichophora by its contraction forces a part 

 of its contents out into latei-al canals in a manner similar to that in 

 Paramecium, and others of the Ciliata, to be described further on. 

 The second family comprises forms highly changeable in outline, and 

 colorless. 



The EuGLENiDJE differs from the Astasidse in having the endoplasm 

 brilliant green, and in having an ingestive apparatus capable of taking 

 only minute particles. Euglena viridis is known by, or has been seen 

 by, every tyro with the microscope. Its developmental forms are so 

 various that it has been described under many names. Stein has ob- 

 , , served a division of the nucleus to take place ; the separate masses in 



Fig. 31.— rracAe^- . . ... 



omonas hispida, some instances acquire an ovate outline, surrounding themselves with 



magnified 600 



a dense coat, while others become thin-walled sacks, full of minute gran- 



