560 



SYSTEMATIC HISTOKY OF THE INFUSOEIA. 



and taper to their extremities, and equal 

 the diameter of the body in length. 

 Found in the dust-like matter upon the 

 siu'face of infusions, and among Confervse 

 and various aquatic plants. Stein asserts 

 that these habitats are those of A. Eich- 

 hornii, not of A. Sol, which does not oc- 

 cm* as a free being. 1-110'" to 1-53.'" 



This species has been very much con- 

 founded with ^. Eichhornii. KoUiker mis- 

 took this last for A. Sol ; and Claparede 

 wrote his description of A. Eichhonu'i, and 

 afterwards discovered it w^as A. Sol that 

 he had investigated. Indeed the brief 

 characters furnished by Ehrenberg are 

 quite inadequate to identify the species. 

 A. Eichhornii (xxni. 29). — Large, 

 white, globose ; tentacles shorter than 

 the diameter of the body, and tapering. 

 The cortical and medullary layers are well 

 distinguished ; the former contains nu- 

 merous vesicles. Tentacles contractile, 

 seen to bend themselves in the prehen- 

 sion of food, &c. Stein affirms that the 

 being which Ehrenberg described and 

 figured under this name is no other than 

 A. Sol, that the tentacles are by no 

 means always shorter than the diameter 

 of the body, but often longer, and that 

 this circumstance of relative length can- 

 not be used in the diagnosis of the spe- 

 cies, but that the conical figure of the 

 tentacles is distinctive. Stein's views 

 on these specific details must be re- 

 ceived cum grano sails ; for the influence 

 of his Aciuetiform h}-pothesis pervades 

 his systematic history of the beings of the 

 class under notice, and his figures of A. 

 Sol prove him to have been in error either 

 in the observation or in the interpreta- 

 tion of the organism ; for they indicate a 

 member of the Acinetina rather than of 

 the Actinophryina. Perty seems to think 

 the largest specimens of A. Sol constitute 

 A. Eichhornii (Ehr.). 



A. oeidata (Stein) (xxni. 24, 25).— 

 Round, more or less discoid, with several 

 concentric circles of vesicular spaces dis- 

 tributed over the smface of the animal- 

 cule, giving it an imdulated outline. The 

 tapering, pointed tentacles arise from the 

 eminences of the smiace, and are equal 

 in length to the diameter of the body, 

 except in small specimens, in which 

 they rather exceed it. The periphery 

 of the body is covered with a homo- 

 geneous, transparent, gelatinous, appa- 

 rently thick layer, within which the 

 large, vesicular, non-contractile spaces, 

 fiUed with water, are found. Besides 

 this superficial layer, a cortical and a 

 medullary substance are clearly pro- 



nounced. The particles of food do not 

 enter the medidlary substance. The 

 finely granular nucleus is cenln-al, sm*- 

 roimded by a rmg of clear medullary 

 matter. Pressm-e, after the action of 

 acetic acid, will sometimes detach it as a 

 free body, invested by a membrane, and 

 having within it an ill-defined granular 

 nucleolus. Diam. 1-38'" to 1-35'". 



A. riridis (Ehr.). — Spherical, greenish ; 

 rays numerous, shorter than the diameter 

 of the body. Diam. of body 1-620'' to 

 1-280". Amongst Confervae. 



A. difformis. — Ii-regulaiiy lobed, de- 

 pressed, and hyaline; rays variable in 

 length, some exceeding the diameter of 

 the body, which is from 1-570" to 1-280". 

 The animalcule thus described Stein ap- 

 prehends to be nothing more than several 

 young specimens of A. Eichhornii con- 

 joined (conjugated). 



A. mar ilia (Duj.). — Differs from A. Sol 

 in its habitat, and in the more marked 

 contractility of its rays. Amongst micro- 

 scopic Algae in the Mediterranean. Pro- 

 bably a mere variety of A. Sol. 



The claim of A. riridis, A. difformis, 

 and A. marina to specific distinction is 

 extremely doubtful. The green colour 

 of the first is immaterial, and the rela- 

 tive length of its rays to the body of no 

 specific importance. The in-egularly- 

 lobed outline of A. difformis, again, is an 

 immaterial condition -, for the soft bodies 

 of true Actinophryina admit a changeable 

 outline, and the reception of food, more- 

 over, to a certain extent involves it. 

 Dujardin justly attributes no other value 

 to his species A. marina, than that it 

 may serve to indicate an Actinophrys 

 living in the sea. 



A. }iedicellata iJ)u].) = PodophrijaJixa. 



A. dirjitata. — (Duj.). — Depressed; rays 

 flexible, thicker at the base, fonning, 

 when contracted, short, thick, finger- 

 like processes. Diam. 1-750". In fresh 

 water containing marsh-plants. Its dis- 

 coid body woidd rather place it with 

 Trichodiscus. 



A. f/ranata (Duj.) (Trichoda graiiata, 

 M.).— Globular, opaque at its centre, stir- 

 rounded by rays of less length than its 

 own diameter. 



A. Discus (J)\\].) = Trichodiscus Sol 

 (Ehr.). 



A. ovata (Lachmann). — A species 

 named by this naturalist in A. N. H. 

 1857, xix. p. 221. 



A. hrevicirrhis (Perty).— Of a dusky 

 yellowish green colour, rarely colourless ; 

 tentacles much shorter than the diameter 

 of the bodv ; not capitate, but bristle- 



