328 ORDER CHOANO-FLAGELLATA. 



in his note-book so long ago as the year 1857, under the designation of an 

 " animalcule with ear-like processes," and which has been since recognized by him as 

 a species closely allied to the Salpingoica amphoridiiun of Professor H. James-Clark. 



The more exact morphological significance of that special organ, the " collar," 

 remains to be discussed. Having due regard to the circulatory currents or cyciosis 

 manifested by the sarcode substance of which it is composed, there can scarcely be 

 room for doubt that this structure finds its precise homologue in the pseudopodia of 

 the Foraminiferous group of the Rhizopoda, and in which a similar circulation or 

 cyciosis of the constituent sarcode is exhibited. Its extreme mobility and plasticity, 

 allowing it at will to be contracted from a widely expanding infundibular contour to 

 a subcylindrical or truncate conical outline, as first recognized by Clark, and shown 

 in many of the accompanying illustrations, or furtlier to be withdrawn entirely into the 

 substance of the body, is of itself indicative of a close relationship with the group just 

 designated. The collar may, in fact, be most appropriately compared in this connec- 

 tion to a funnel-shaped aggregation of the single anteriorly protruded pseudopodic 

 fascicle of some Monothalamous Foraminifer such as Lagcna or Miliola,^ or it may 

 be supposed that such a type has developed a single subcylindrical anterior pseudo- 

 podium, whose substance has become hollowed out centrally, so as to produce a 

 tubular or infundibuliform contour. In either case the central flagellum may be 

 regarded as a supplementary appendage, whose presence alone secures the group of 

 the Choano-Flagellata from being placed among, or closely adjacent to, such typical 

 Rhizopoda. 



Comparatively small as is the number of species that have so far been referred to 

 this Discostomatous or collared Flagellate section, the multiplicity of forms presented 

 by them is truly remarkable. Still more noteworthy, however, in this connection, 

 is the extraordinary similarity that subsists between these various modifications 

 and conditions of growth, as here exhibited, and those found to obtain among the 

 more highly organized Peritrichous group of the Vorticellida^. Like these latter, 

 the great majority of its members pass a sedentary existence, and are similarly 

 distinguished under such conditions for their solitary, or social and dendritic habits 

 of growth, for their secretion and occupation of distinct horny loricae, or for their 

 colonial aggregation within a common gelatinous matrix or zoocytium. Compared 

 in detail with one another, the isolated representatives of the genus Monosiga may 

 aptly be likened to those of Vorticella or Rhahdostyla, Codosiga to Epistylis or 

 Operadaria, Salp'uigmca to Vagbiicola or Cot/iuniia, while in Phalansteriuiii and 

 Protospongia the conditions presented find their precise parallel in OpJirydium. 

 It would seem by no means unreasonable, indeed, to regard these diversely modi- 

 fied Flagellata as the lineal ancestors or archetypes of the Peritrichous series, 

 and it has been already suggested by Gruber* that the funnel-shaped collar of the 

 present Flagellate series finds its morphological counterpart in the delicate trans- 

 parent membrane lying within the peristome of many ordinary Vorticellidae, and 

 which seen in profile presents the aspect of a setose appendage. A still closer 

 approximation is, however, undoubtedly found in E. Ray Lankester's anomalous 

 genus Torquatdla, where an extensile and contractile collar-like membrane takes 

 the place of the normal circular fringe of cilia. As demonstrated in various 

 instances in the course of this treatise, the primitive condition of the adoral fringe 

 or wreath of cilia is that of a simple membranous band or expansion ; and accepting 

 the phenomena thus exhibited by the life -history of the zooid or individual as in 

 all probability indicative of the developmental cycle or phylogeny of the group or 

 order, it may be consistently inferred that the Peritrichous series originated from a 

 stock or phylum in which the now highly specialized adoral ciliary wreath was repre- 

 sented by a simple infundibuliform membranous expansion. While the genus Torqiia- 

 tella affords substantial evidence in favour of this interpretation, still more important 

 testimony in the same direction is perhaps yielded by the two Cilio-flagellate types 

 Stepliajwmonas and Astlwiatos. Both of these, while possessing an anteriorly located 



* ' Zeitschrift fitr Wissenschaftliche Zoologie,' Bd. xxxi., 1879. 



