120 r. W. PHILLIPS — NOTES ON THE 



monads, and the increase of size is effected in this manner. The 

 astonishingly rapid growth of the Infusoria is truly wonderful. 

 Ehrenberg computed that in the case of one animalcule (Sii/lo- 

 ni/chia mytilus) no less than one million of independent beings were 

 derived from the simple and repeated fission of a single zooid in 

 the course of ten days ; and in another {Paramecmm aurelia), he 

 reckoned that 268 millions might be similarly developed within a 

 single month. Substantial evidence of this prodigious increase is 

 afforded by the Spongida, and the other previously-mentioned 

 examples, each colony representing the binary division of a single 

 unicellular zooid. 



I have never seen any instance of gemmation. It is, I believe, 

 the rarest method of reproduction ; and I believe is unknown in 

 the pantostomatous section. Sporular multiplication is much more 

 common. The term is applied to those reproductive phases in 

 which the animalcule assumes a quiescent encysted condition, and 

 subseqiiently bursts into a Jiumber of spore-like bodies. In some 

 instances the number of spores may be counted, and will be found 

 to vary in numbers of two, four, eight, sixteen, and thirty-two, 

 when they are termed macrospores ; but when they exceed this 

 number and are innumerable, they are called microspores. In some 

 instances many thousands of these spores are included in the parent 

 capsule, or sporocyst, as it is called, and so extremely minute is 

 their individual calibre that even with the highest powers of the 

 microscope their individuality cannot be discerned. 



In both cases each particle or spore ultimately developes to the 

 parent form. 



This sporular stage of existence is at the present time attracting 

 the attention of the most eminent biologists ; new and startling 

 facts are continually recorded, showing its universal prevalence, 

 and the important part it plays in the origin of diseases. 



Having now arrived at some idea of the organisation of the In- 

 fusoria, we will, after a few words on their distribution, turn our 

 attention to those species which have been observed in the neigh- 

 bourhood. 



The majority of the Infusoria are to be found either in fresh or 

 salt water, either free-swimming, attached to submerged plants 

 and other objects, or parasitically attached to other living organ- 

 isms ; many of these do not, as in the ordinary cases of parasitism, 

 maintain themselves at the expense of their host, nor are they in 

 any way injurious, but are simply co-associated, merely using the 

 ectoplasm of their host as a fulcrum of attachment. For these 

 habits Prof. Van Beneden has invented the title of commcnsalism. 

 The Entomostraca are generally the entertainers of these guests. 

 Mr. Saville Kent considers that the Daphniadae, or water-flea 

 tribe, are an exception to this rule, but about a month ago I came 

 across an example {Daphnia vetula) which was covered with para- 

 sites. It must not, however, be considered that the Infusoria are 

 to be found in water only. All the Opalinidte lead a parasitic life 

 within the alimentary canals of frogs and other Amphibia. The 



