Untitled

! I0 ORGANIZATION OF THE INFUSORIA.invariably attached to other living organisms, are not maintained at theexpense of the essential juices of these latter, but simply occupy withrespect to them the position of co-lodgers or messmates. The veryappropriate title of "commensals" has been recently employed by Prof.P. van Beneden to distinguish those organisms among the higher Metazoicseries which pass a similar co-associated, non-hurtful, and often mutuallydependent existence, and that of " commensalism " for the distinction ofthe peculiar pseudo-parasiticlife habits which they exhibit. As might beanticipated, the phenomenon of commensalism is exhibited among theInfusoria chiefly by those types that lead a fixed or sedentary existence,and isnotably conspicuous among the Peritrichous Vorticellidae. Fromthese may be selected as examples various species of the several generaEpistylis, Zoothamnium, Opercularia, Cothurnia, Scyphidia, and Spirochona,a very large number of which are found in company only with certainspecies of aquatic Insecta, Crustacea, or Mollusca.As free or unattached messmates or commensals, reference may be moreespecially made to the family of the Urceolariidae, including Trichodinapediculus, notable for its intimate relationship with the fresh-water Hydra,and which positionit shares with the Hypotrichous form Kerona polypornui.Other animalcules of the same family, exhibiting closely correspondinghabits, are rep'resented by the two genera Urceolaria and Trichodinopsis ,while a near ally, Licnophora, has been found as yet as a commensal only ofcertain marine Planarians. The genus Ophryodendron, among the Tentaculifera,furnishes in the two species O. sertularia and O. multicapitatamarked examples of pseudo-parasitic life, the former being a commonguest of both Sertularian zoophytes and the little hairycrab Porcellanaplatycheles, while the latter, recently discovered by the author, has as yetbeen found attached only to the limbs and carapace of a species of sessileeyedcrustacean. Descending to the division of the Flagellata, commensalism,so far as is at present known, would appear to be most abundantlyrepresented among the mostly sedentary collar-bearing section of theChoano-Flagellata, where it is further noteworthy that the majority arefound attached, as commensals, to the peduncles or loricae of other higherInfusoria. In this manner Salpingoeca minuta is found in society with theflagellate type Dinobryon sertularia, while Salpingoeca convallaria grows onEpistylis anastatica, and Monosiga Steinii on Vorticella convallaria andEpistylis plicatilis, itself a commensal of the common pond-snail.While the foregoing summary of some of the more abnormal areas ofdistribution of the Infusoria subserves the purpose of indicating to thestudent and collector of this group of beings the localities in which to seekwith success forcertain specific or generic types, a brief space devoted toan enumeration of the most favoured habitats of the non-aberrant typeswill probably be welcome. In this direction it need scarcely be indicatedthat weedy ponds, and slowly running water, containing an abundance ofaquatic plants, present both the most accessible and most remunerative