448 THE PROTOZOA 



also ciliated. These excretory systems of Opalina and Pycnoihrix differ in 

 being endoplasmic from the ordinary contractile vacuoles, which are always 

 formed in the ectoplasm. 



The endoplasm of the Ciliata may contain enclosures of various kinds : 

 food -vacuoles ; metaplastic bodies in the form of excretory grains, crystals, 

 pigment-grains, etc. ; zoochlorellae, and occasionally parasites of one kind or 

 another, etc. Special attention has been drawn by Faure-Fremiet (38'5 and 

 835) to the bodies termed by him spheroplasts, and considered by him to be 

 homologous with the mitochondria (p. 41). The bodies in question are 

 small spherules, which multiply by fission when the cell- body divides ; they 

 are permanent cell-organs to the same extent as the nuclear apparatus, of 

 which, however, they are entirely independent. 



As pointed out above, the form of the macronucleus and the number of 

 nuclei vary greatly in different species. The cases will be considered below 

 in which the micronucleus appears to be wanting (Opalina), or is contained 

 in the macronucleus in the ordinary condition of the body (Trachdocerca, 

 Ichthyophthirius). As a rule the macronucleus has a finely granular appear- 

 ance, with the chromatin distributed evenly over the nuclear framework ; 

 but in a few cases it has a distinctly vesicular structure, with a large karyo- 

 some, as in Loxodes (Joseph, Kasanzeff), Chilodon (Nagler, 96), etc. The 

 macronucleus divides by binary fission of a simple and direct type (Fig. 54). 

 The micronucleus, on the other hand, divides by mitosis (Fig. 61). In 

 Trachdocerca, a form which may possess one or many nuclei (but no separate 

 micronuclei), Lebedew (93) describes a peculiar mode of multiplication of the 

 nuclei, which divide by multiple fission to form a morula-like body consisting 

 of a mass of small nuclei which separate from one another (Fig. 66). In 

 Loxodes, another form in which the number of nuclei varies greatly in different 

 specimens, the macronuclei do not divide, but only the micronuclei do 

 so, and the macronuclei arise by growth and modification of the micro- 

 nuclei (Kasanzeff). In many cases in which the macronucleus is of the 

 elongated moniliform type, or in which the body in the ordinary state contains 

 two or more macronuclei, they come together to form a single compact 

 macronucleus prior to division; but in other similar cases this does not occur, 

 and when the body divides the nuclei are distributed irregularly between the 

 two daughter-individuals, as in Trachdocerca, Opalina, etc. The distributed 

 form of nucleus is especially characteristic of the astomatous parasitic forms, 

 and in the opinion of Pierantoni (A.P.K., xvi., p. 99) is correlated with nutri- 

 tion by the osmotic method. 



The micronucleus is less variable in form or number, as a general rule, 

 than the macronucleus, but is not infrequently multiple, especial! y when there 

 is more than one macronucleus ; but in Trachdius ovum a single large macro- 

 nucleus is combined with thirteen micronuclei (Hamburger, 841). 



The conjugation of the Ciliata conforms, as a general rule, in its main 

 outlines to the scheme sketched out above (Fig. 77), but some important 

 variations must be noted. In the first place, the conjugation is often pre- 

 ceded % by active division of the animals, so that the conjugants* are much 

 smaller than the ordinary individuals of the species. When the two conju- 

 gants come together, the micronucleus of each usually divides into four, but 

 sometimes into eight, as in both conjugants of Euplotes and the microconju- 

 gant of Peritricha ; in either case, however, only one micronucleus persists, 

 and furnishes the two pronuclei. 



The Peritricha exhibit in their conjugation certain peculiarities which are 

 clearly of a secondary nature and correlated with their sedentary habit. 

 Certain individuals divide two or three times successively to produce four or 

 eight microconjugants (" microgametes ") which acquire a ring of locomotor 



* It is preferable not to speak of two conjugating Infusoria as gametes, since 

 it is very doubtful if they correspond to the gametes in the other classes of Protozoa. 

 It is on the whole more probable that the conjugants correspond rather with 

 gamonts or gametocytes, which originally produced a number of gametes, reduced 

 now to two, represented in each conjugant by the two pronuclei. 



