INFUSORIA. 



[ 345 ] 



INFUSORIA. 



may be mentioned that Ehrenberg regards 

 the Infusoria as hermaphrodite ; the male 

 organs consisting of the contractile vesicles 

 and the so-called nucleus ; whilst the ova- 

 ries and ova are represented by colourless or 

 coloured corpuscles imbedded in the sub- 

 stance of the body, and which are found to 

 vary in number periodically, being sometimes 

 absent, at others forming filiform meshes 

 comparable to the ovaries of Insects and the 

 Trematoda. Undoubtedly, many of the co- 

 loured corpuscles seen in the bodies of the 

 Infusoria are granules of chlorophyll, or 

 other matters derived from without; but 

 some of them may consist of chlorophyll- 

 granules formed within the body, as inHydra. 

 Division. — Spontaneous division is either 

 longitudinal (PI. 25. fig. 37), or transverse 

 (fig. 38). In both the nucleus undergoes 

 division, as well as the body. In the longi- 

 tudinal division the process commences at 

 one end of the body, from which the cilia 

 usually are retracted or disappear ; a notch 

 is first perceived, which afterwards becomes 

 deeper, until the body is completely cleft ; 

 the two halves then acquire cilia, and assume 

 the functions of perfect animals. In the 

 transverse division, a median constriction 

 appears first, followed by perfect separation, 

 as in the last. During these processes of 

 division, the animals sometimes continue 

 their movements as usual ; at others this is 

 more or less interfered with. In Vorticella 

 (PI. 25. fig. 21 a), in which the process of 

 lono^itudinal division mav be couvenientlv 

 watched, on account of the comparative fix- 

 ture of the animals by a pedicel, when the 

 division is nearly completed, a ring of cilia is 

 formed near the attached end of the body, 

 by the movements of which the new Vorti- 

 cella is separated from the parent. The 

 process is completed in about an hour. 



Gemmation — is not a general process in the 

 Infusoria. It is well seen in Vorticella (PI. 

 25. fig. 26). The buds arise from near the pos- 

 terior end of the body, and, when fully deve- 

 loped, liberate themselves by the formation of 

 a posterior ring of cilia, as above mentioned. 



Diffluence. — Some authors have described 

 a mode of increase in Infusoria, where the sub- 

 stance of the body breaks up into a number 

 of fragments, each of which is capable of 

 becoming a perfect individual. The exist- 

 ence of this process, called diffluence, is 

 questioned by later observers, and is said to 

 have arisen from a confusion with the phse- 

 nomena accompanying the increase of the 

 encvsted forms. 



Encysting Process. — Many of the Infusoria 

 are observed to alter their form at certain 

 periods, become rounded, lose or retract their 

 cilia (PI. 25. fig. 27), and to secrete all over 

 their sm*face gelatinous matter, forming a 

 coat or cyst enclosing them. While thus 

 encvsted, the substance of the bodv becomes 

 divided, and gives origin to a number of in- 

 dividuals, which are discharged by the burst- 

 ing of the cyst. They do not always re- 

 semble the parent in form (PI. 25. fig. 34). 

 In some cases the progeny or brood become 

 individually encysted within the parent cyst; 

 it appears, however, that they are not dis- 

 charged in this condition, but esca])e first 

 from their own cyst and then from the pa- 

 rent, in which they leave their own exuviae. 

 Stein thinks that it was such broods that 

 Ehrenberg mistook for the results of the 

 increase by diffluence. 



The encysted forms also propagate by 

 giving birth to germs by a process of internal 

 or external budding; this connected with the 

 Acineta-formation. — The most remarkable 

 point connected with the reproduction of the 

 Infusoria is the phaenomenon of the Alter- 

 nation OF GENERATIONS. Many kinds 

 which propagate by subdivision, or gemmation 

 from the surface, in their ordinary course of 

 life, as Vorticella, Faramecium, &c., undergo 

 a metamorphosis leading to a difi'erent mode 

 of increase. They lose their characteristic 

 form, become rounded and encysted, and 

 then push out tentacular processes at various 

 points, so as to acquire the shape which has 

 given rise to the foundation of the genus 

 Acineta. Occasionally the Vorticellce of this 

 form, which after becoming enc3sted are 

 detached from their pedicels, become again 

 attached by a foot, and in this case present 

 the appearance of a Podophrya. The nucleus 

 and the contractile vesicle are clearly di- 

 stinguishable in this stage. The nucleus 

 then gives birth to a new individual, by bud- 

 ding, which becomes free and independent 

 in the interior of the Acineta pai'ent, and is 

 ultimately expelled. This process may be re- 

 peated many times. Propagation also occm-s 

 in these Acineta ovPodophrya forms by a bud- 

 ding out from the surface, or the conversion 

 of the whole contents into new individuals. 



We may sum up the modes of increase 

 of the Infusoria as follows : — 1. The perfect 

 characteristic form of the animal may in- 

 crease by simple division, or by gemmation 

 from the surface. 2. This form may be- 

 come rounded and encysted ; the encysted 

 mass is then («) converted entirely into a 



