282 



THE SPOROZOA 



times vacuolated, and often coloured. It contains numerous 

 enclosures and metaplastic products, most frequently of an oily 

 or fatty nature, representing probably reserve nutriment. In the 

 youngest trophozoites there is but a single nucleus, but with 

 growth of the parasite the number of nuclei lodged in the 



Fio. 88. 



Extremity of a trophozoite 

 of Myxidium lieberkiihnii, 

 Biitsch'li (par. Esox and Lota), 

 in which no spores are as yet 

 formed, x 750. e, e', ecto- 

 plasm, homogeneous at e, 

 vertically strutted at e' ', n, 

 nuclei ; g, globules of fat 

 blackened by osmic acid. 

 (After Thelohan, from Wasie- 

 lewski.) 



endoplasm continually increases by their division, until many are 

 present in the full-grown forms. The number is smallest in 

 disporous forms (infra, p. 283), where it may be no more than ten, 

 but usually it is much greater than this. The nuclei are very minute 

 as a rule, generally not more than 1-2 //, in diameter, but they 

 sometimes differ markedly in size in the same individual. Each 

 nucleus consists in typical instances of a deeply-staining membrane 

 enclosing a reticular framework, on which the chromatin is partly 



"AU: 



a b c d e 



FIG. 89. 



Stages in nuclear division in Chloromyxum leydigi, Ming. The resting nucleus (a) contains 

 chromatin granules and a " chromatosphere." Preparation for division commences (ft) by the 

 breaking up of the chromatosphere. In the next stage (c) the chromatin collects towards the 

 transverse plane of the nucleus, to form (d) the equatorial plate, which splits to furnish the 

 chromatic substance of (e) the two daughter nuclei. (After Doflein.) 



diffuse, partly aggregated towards the centre to form a " chromato- 

 sphere." True nucleoli or karyosomes are not found. The division 

 of the nuclei takes place by a form of karyokinesis, but without 

 asters or centrosomes (Fig. 89). 



(2) Spore-Formation. The spores commence to develop at an 

 early stage in the growth of the trophozoite, and in some species 

 they continue to be formed until the whole of the substance of the 

 trophozoite is used up in their production. In other cases, how- 

 ever, the volume of the reproductive bodies is small in comparison 

 with that of the whole body. The spores may be few in number, 



