lOO ORGANIZATION OF THE INFUSORIA. 



preceding case, and, as the comparisons instituted are as between cell 

 and cell or equivalent appendages of such cells, all likenesses of this 

 description may in the strictest parlance be termed homologous resem- 

 blances. Some of the more prominent examples that fall within this 

 last-named category may be first enumerated. Commencing with the 

 Infusorial group, in its simplest or most lowly organized condition, or in the 

 first place descending yet a step lower, and selecting a simple Rhizopodous 

 Protozoon, such as an Amoeba, it is impossible not to recognize that we have 

 here the morphological equivalent or homologue of a tissue-cell in its most 

 elementary condition, as represented by a colourless blood-, lymph-, or 

 ganglionic-corpuscle. The likeness in this instance is, furthermore, not 

 simply one of form ; in the case of the blood- and lymph-corpuscles, reptant 

 movements accomplished by the extension and contraction of pseudopodic 

 appendages, and similar to those of the independent Rhizopod, are also 

 freely manifested. It is from such a similar simple repent amoebiform body 

 that many of the flagelliferous members of the Infusorial class take their 

 origin, as demonstrated by the author in the case oi Eiiglena, Etttreptia, and 

 many Choano-Flagellata, while the retrogression to such a simple elemental 

 type is a familiar phenomenon among the representatives of this same section 

 immediately antecedent to the process of either encystment or coalescence. 

 Proceeding with an examination of the flagelliferous section of the Infusoria 

 in its normal conditions of development, we find at the bottom of the series 

 the curious genus Trypanosoma distinguished in the case of T. Eberthi by 

 a long attenuate body, around which is spirally disposed a most delicate 

 frill-like membrane, whose active vibrations fulfil the function of locomotion. 

 It is a remarkable fact that an essentially similar type of structure charac- 

 terizes the exceptionally shaped monocellular spermatozoons of Triton, 

 Bovibinator, and other tailed and tailless Amphibia, as originally figured 

 by Wagner and Leuckart, Unker, and Von Siebold. Spermatozoa in their 

 normal and most familiar form consist merely of a more or less rounded 

 anterior extremity or head, and a dependent flagelliform appendage or tail, 

 and have been recently compared by Professor Huxley * to a simple cell 

 of which the larger and more solid anterior part represents the nucleus, 

 and the dependent tail only the very fully developed and much attenuated 

 peripheral protoplasm. This more normal and simple form of the sper- 

 matozoal element is abundantly represented in the class now under con- 

 sideration. Such simple uniflagellate types as Monas and Petalonionas 

 exhibit in their adult state of development a type of structure essentially 

 corresponding with that of an ordinary spermatozoon, while the Hctcromitcu, 

 the majority of the Choano-Flagellata, and numerous Eustomatous 

 Flagellata commence their existence as simple uniflagellate spermatozoon- 

 like organisms. In the case of Hetcromita lens, as also in that of the 

 swarm-gemmules of the flagelliferous Spongozoa, it is, moreover, noteworthy 

 that in their initial condition of free-swimming existence the individual 



* Biological Lectures, South Kensington, Session 1879-80. 



