ZOOLOGICAL AFFINITIES. lOI 



unicellular zooids are aggregated together in clusters, closely resembling 

 the sperm-bundles of various higher animals, the same being similarly- 

 derived from the repeated cleavage or fission of a primarily single unit. 

 Illustrations of the homoplastic likeness that subsists between certain 

 Infusoria and the more complex forms of spermatozoidal structures are 

 afforded by the Heteromitcs in their adult and bi-flagellate condition, in 

 which they resemble in a remarkable manner the so-called " zoospores " 

 or " antherozooids " of various cryptogamic plants, while in the Poly- 

 mastigous forms Pyramimouas and Chloraster the modification presented 

 is almost identical with that which obtains in the spermatic elements of 

 Hoinarus and other Podophthalmous Crustacea. 



The next recurring structural homotype in the ascending scale as repre- 

 sented by independent Infusorial organisms with relation to the differentiated 

 elements of a compound tissue-structure, is met with in the remarkable 

 multiflagellate type discovered by Professor Haeckel, and which has re- 

 ceived from him the title oi Magosphcera. In this instance the isolated zooids 

 of the normally compound globose colony present a somewhat elongate 

 pyriform contour, and bear at their truncate anterior extremities a number 

 of long whip-like appendages or flagella. A type of structure in all ways 

 comparable with the zooids of Magosphcera is repeated in the ciliated 

 epithelium-cells of all higher tissue organisms, from which, compared 

 separately, they are scarcely to be distinguished. One more illustration 

 in connection with the present line of comparison remains to be cited. 

 Many Flagellata, such as Spongomonas, PJialanstcriwn, and Uroglena, are 

 distinguished for their excretion of a glairy gelatinous matrix, within 

 the substance of which the separate units multiply by the process of 

 binary segmentation, and gradually extend the limits of their common 

 domicile. A similar building up by excretion of a common gelatinous 

 matrix, and the extension of the boundaries of the mass by repeated fission 

 within the same, is the essential characteristic of the cartilage cells of 

 both Vertebrata and Invertebrata. The comparison here instituted is, how- 

 ever, still more striking in the case of Nostoc and other allied plants. In 

 these latter the condition of simple nucleated cells, imbedded like those of 

 cartilage cells in the midst of a common gelatinous matrix, is generally 

 exhibited, while in that of the Infusoria it obtains only during the 

 duplicative process. 



As might have been anticipated, it is among the lower or flagelliferous 

 section of the Infusoria only that are encountered those forms that find their 

 counterpart in the component elements of the higher tissue-structures now 

 enumerated ; in a similar manner it will be found that those homoplastic 

 prototypes of certain Metazoic organisms, taken as a whole, exist only 

 among the ranks of the more highly differentiated Ciliate and Tentaculi- 

 ferous divisions of the group. 



Before proceeding, however, to an enumeration of these more highly 

 differentiated homoplasts, it has to be shown that both the Flagellate and 



