INFUSORIA. 837 



individuals. The function of the slender elongate zooids of Z. altcrnans 

 and Epistylis ophioidea is not known. 



Gemmation is rare. It is the sole mode of reproduction observed in 

 Spirochona gemmipara, and may be exhaustive of the parent. It occurs 

 also in Stylochona nebalina, Lagenophrys ampulla, and in some species of 

 Vorticella, e.g. V. microstoma. The free-swimming bud is unlike its 

 parent ; in Lagenophrys it is Hypotrichan in its ciliation (Stein), or 

 provided with a terminal ciliary wreath (Plate) ; in Vorticella it resembles 

 a rosette microzooid (sttprd), and has a similar destiny. 



The term spore-formation is applied to the production by fission of 

 small individuals within a cyst. The number produced varies from two in 

 Prorodon teres and Amphileptus to 16 in Chilodon cucullulus, or even 

 1000 and upwards in Ichthyophthirius multifiliis, an ectoparasite on some 

 freshwater fish. Encysted Vorticellids with many nuclei have been 

 observed. In Vorticella nebulifera Everts saw emerge from the cyst 6-10 

 minute globular bodies each with a ciliary girdle and in its centre a mouth. 

 They multiplied by fission, but eventually affixed themselves by the oral 

 end, developed a peduncle and ciliary disc. The young Ichthyophthirius 

 is unlike its progenitor. Small Infusoria differing from the adult form have 

 been observed, but whether produced from cysts or not is not known 1 . 



Conjugation is universal and for the most part temporary. The con- 

 jugating individuals are as a rule small in size, produced by rapidly 

 repeated fission. They unite by their oral aspects, e. g. in Paramecium, 

 Stentor, or by their lateral as in Hypotricha. The union brings about 

 changes ; the nucleus is broken up ; the paranuclei divide with mitosis ; pro- 

 toplasm may be interchanged as well as paranuclei (p. 835 and note 2, ante), 

 the cilia may be withdrawn, the peristome obliterated. Separation brings 

 .about a reconstitution of all these organs, followed by growth or re- 

 juvenescence. Permanent conjugation ( = copulation of Engelmann) is met 

 with in Stylonychia and some other Hypotricha, and in some Vorticellina. 

 In Vorticella and Epistylis it takes place between a microzooid, whether a 

 fission-product or a bud, and an ordinary individual 2 . It is followed by a 



1 Everts looked on the reproduction of V. neJmlifera as an instance of Alternations of Generations. 

 Dimorphism may affect the ordinary fission-product, e. g. Folliculina {Freja) ampulla, according to 

 Mb'bius, undergoes unequal longitudinal fission, and the part set free is uniformly ciliated, but when 

 settled developes its bilobed peristome and Heterotrichan ciliation (Biol. Centrablatt. vi. p. 540). 

 The so-called internal germs are probably always due to parasites, or to diseased nuclear products, 

 caused by Bacteria. See on the whole subjects, Engelmann, M. J. i. pp. 584-602 ; Biitschli, Abhandl. 

 Senck. Ges. x. pp. 343-55 ; van Rees, Z. W. Z. xxxi. 1878. 



3 See Engelmann, M. J. i. pp. 582, 622, 624, and summary, p. 628 et seqq. In Epistylis flavicans 

 he states that a zooid A. gives rise by fission to two zooids B.B. Of these, one is resolved into 

 microzooids. The detached microzooid always conjugates with an individual B, never with A. 

 Hence he concludes there is a sexual distinction ; the microzooid is male, the zooid B. female. 

 Engelmann' s statement that the paranucleus is absent in Vorticellina appears to be wrong : nor 

 has it the sexual value which he and other authorities of the time supposed. 



