THE INFUSORIA 



383 



Fio. 30. 



or oral extremity is decidedly smaller than the other. In Hoplito- 

 phrya the division is also unequal, but the smaller individual is at 

 the end usually regarded as the posterior end. 

 In Anoplophrya nodulata there is multiple transverse 

 fission (Fig. 20), the result being one large in- 

 dividual and four or five smaller ones. Similarly 

 in Opalinopsis the posterior end of the body gives 

 rise to a series of small individuals which constrict 

 off from the parent. 



The mode of reproduction in Spirochona is very 

 remarkable. A large lump grows from the body 

 wall just behind the spiral membrane (Fig. 23), 

 and this increases until it reaches a size almost 

 as large as the parent form. Judging from ex- 

 ternal appearance alone, it might be considered 

 that this is a process of gemmation essentially 

 different from the transverse fission of the HOLO- 

 TRICHA, but the meganucleus and the micronuclei 

 divide equally during the growth of the so-called 



j j. , i i Anoplophrya nodu- 



bud, and no difference can be observed in size or lata, o. F. Muiier, from 



quality between the nuclear portions that are dis- chaetaTexhfbiUn^'un- 



tributed to the two resultant individuals. The j^ al and^dhrisfon^of 



process cannot therefore be separated from fission, the elongated mega- 



. , ,. ., e ,1 . ,1 f nucleus (M, M) with- 



notwithstanding the tact that tne manner 01 out previous concen. 

 growth of the parent antecedent to reproduction numerous Contractile 

 is very exceptional. In the VORTICELLINA the vacuoies. (After ciap. 



J , ' . . n i i and Lachmann.) xca 



manner of reproduction is usually designated iso. 

 longitudinal fission. The external phenomena 

 begin with the division of the spiral zone into two equal spirals, 

 and proceed through the disc to the stalk, and may (in some of 

 the solitary forms) continue to the base of attachment, or (in the 

 colonial forms) be arrested before the attached end of the stalk is 

 reached. In the majority of the solitary Vorticellina the stalk does 

 not divide. The left daughter individual develops an aboral ring of 

 cilia and swims away, whilst the right daughter individual remains 

 with the parent stalk intact. 



There is not any morphological distinction between the longi- 

 tudinal fission of the PERITRICHA and the transverse fission of the 

 HOLOTRICHA. It is very probable that, if there is any justification 

 at all for the comparison of the body axes of such simple forms of 

 life, the longitudinal axis of PERITRICHA is homologous with the 

 dorso-ventral axis of the HOLOTRICHA, and the fission is from a 

 morphological point of view a transverse fission. 



The examples of unequal transverse fission which have been 

 quoted as occurring in HETEROTRICHA lead to the consideration of 

 an interesting modification of the process which occurs in the 



