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100 ORGANIZATION OF THE INFUSORIA.preceding case, and, as the comparisons instituted are as between celland cell or equivalent appendages of such cells, all likenesses of thisdescription may in the strictest parlance be termed homologous resemblances.Some of the more prominent examples that fall within thislast-named category may be first enumerated. Commencingwith theInfusorial group, in its simplest or most lowly organized condition, or in thefirst place descending yet a step lower, and selecting a simple RhizopodousProtozoon, such as an Amoeba, it is impossible not to recognize that we havehere the morphological equivalent or homologue of a tissue-cell in its mostelementary condition, as represented by a colourless blood-, lymph-, organglionic-corpuscle. The likeness in this instance is, furthermore, notsimply one of form in the case of the blood- and;lymph-corpuscles, reptantmovements accomplished by the extension and contraction of pseudopodicappendages, and similar to those of the independent Rhizopod, are alsofreely manifested. It is from such a similar simple repent amcebiform bodythat many of the flagelliferous members of the Infusorial class take theirorigin, as demonstrated by the author in the case of Euglena, Eutreptia, andmany Choano-Flagellata, while the retrogression to such a simple elementaltype is a familiar phenomenon among the representativesimmediately antecedent to the process of either encystmentof this same sectionor coalescence.Proceeding with an examination of the flagelliferous section of the Infusoriain itsnormal conditions of development, we find at the bottom of the seriesthe curious genus Trypanosoma distinguished in the case of T. EbertJd bya long attenuate body, around which is spirally disposed a most delicatefrill-like membrane, whose active vibrations fulfil the function of locomotion.It is a remarkable fact that an essentially similar type of structure characterizesthe exceptionally shaped monocellular spermatozoons of Triton,Bombinator, and other tailed and tailless Amphibia, as originally figuredby Wagner and Leuckart, Unker, and Von Siebold. Spermatozoa in theirnormal and most familiar form consist merely of a more or less roundedanterior extremity or head, and a dependent flagelliform appendage or tail,and have been recently compared by Professor Huxley * to a simple cellof which the larger and more solid anterior part represents the nucleus,and the dependent tail only the very fully developed and much attenuatedperipheral protoplasm. This more normal and simple form of the spermatozoalelement isabundantly represented in the class now under consideration.Such simple uniflagellate types as Monas and Petalomonasexhibit in their adult state of development a type of structure essentiallycorresponding with that of an ordinary spermatozoon, while the Heteromita,the majority of the Choano-Flagellata, and numerous EustomatousFlagellata commence their existence as simple uniflagellate spermatozoonlikeorganisms. In the case of Heteromita lens, as also in that of theswarm-gemmules of the flagelliferous Spongozoa, it is, moreover, noteworthythat in their initial condition of free-swimming existence the individual* Biological Lectures, South Kensington, Session 1879-80.