H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 331 



during reptation, — nor could we expect to find it there upon being referred to its horuolog- 

 ical relation to the asymmetrically attached gubernaclum of Anisonema, — it none the less 

 belongs to the reptant side of the animal, and as it were, controls its motions, and acts as a 

 keel upon which the posterior end of the body vibrates and reels from side to side. Finally, 

 in reference to this point, it may be added, that this species does not swim, properly speak- 

 ing, nor has it the character of the revolving natant forms, such as Dujardin separated from 

 the Astasia of Ehrenberg, and described under the name of Peranema. 



For the sake of accumulating and multiplying diagnostic characters, that shall serve us 

 hereafter as discriminative points in determining the classificatory relations of Flagellcda, it 

 is most desirable that every critical study of one of these forms should be carefully recorded, 

 even to the minutest details. On this account, therefore, and particularly in the present 

 connection, notwithstanding that this species is so frequently met with, and apparently so 

 well known, it will not be out of place here to describe it anew ; especially as some of the 

 features presented for the consideration of naturalists are not in accordance with the in- 

 terpretation put upon them by previous observers. 



The bod// of this animalcule is colorless, but frequently has a slight yellowish or reddish 

 tinge, which is derived by diffusion from the granular contents of the interior. The only 

 legitimate color present lies in the very faint red eye-spot (s). The form is variable from 

 elongate ovate to cylindrical, with a gentle taper, at the anterior third, into a narrow, trun- 

 cate-emarginate head. Posteriorly the dorsal region is rounded, but on the ventral face a 

 broad, triangular prolongation (Jl 2 ) — already spoken of as the homologue of the gubernaclum 

 of the reptant Hderonemata — extends backward beyond the outline of the dorsum. The 

 exact relation of this prolongation to the axis of the body is not to be determined beyond 

 a doubt, because of the constantly shifting attitude of the animal ; at one moment the 

 gubernaclum (Jl 2 ) is on the left, and then at the next instant it appears on the right of the 

 mesial line, or follows for a while between these two points, according as the body keels 

 over more or less from one side to the other, or balances itself in a median position. It 

 appears most frequently, however, to be unilateral. 



The amoeboid contortions (fig. 46) of the body have already been mentioned, but I would 

 add that this is only a resemblance, a mere suggestion, if one may use the term, of the 

 mode of locomotion of Amoeba ; for it is not, as in the latter, an actual flowing out of a glairy 

 mass into protean, reptant processes, but an exceedingly variable puckering, and always ac- 

 companied by a longitudinal contraction of the body ; the one being evidently necessary to 

 the other. If I may carry out the niceness of distinction further, I should say that whilst 

 Amoeba is contractile and plastic, Astasia is retractile and flexible. 



The flagellum (Jl) also, by its subterminal attachment to the head, carries out the typical 

 plan of the reptant Heteronemata. It is based strictly on the ventral side of the front, de- 

 scending from the latter with such an abrupt turn forward that it appears, without close 

 observation, to be a mere tapering prolongation of this region. Yet it is neither related to 

 the body in the latter sense, nor an extension of it from any point of view, but is as strictly 

 an appendage as any form of vibratile cilia, 1 and alike as incapable of contraction. It is so 



l As my views in regard to the relation of vibratile cilia to ings of the Boston Society of Natural History, for September, 



underlying cells may not be fully understood in this allusion, I 1863, p. 283, and republished in the Annals and Magazine of 



would refer to my published opinion of this subject, in a note Natural History, for December, 1864. 

 appended to some remarks upon Actinojihrys, in the Proceed- 



