68 



MORPHOLOGY AND CULTURE OF MICROORGANISMS 



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FIG. 50. Successive stages of 

 copulation and sporulation in Schizo- 

 saccharomyces octosporus. 



described, with one nucleus and one or more metachromatic vacuoles 

 containing corpuscles (Fig. 50, a) . Fusion takes place between the two 

 cells which are nearest together. Each of these two cells sends out a 

 tiny beak; the two little beaks thus formed anastomose and form a 



channel of copulation joining the two 

 cells (Fig. 50, b, c, d). The septum 

 separating the two gametes in the 

 middle of the channel is quickly 

 absorbed, and the two cells then 

 have free communication. The cyto- 

 plasm of the two cells draws together 

 and mingles in the channel; there the 

 two nuclei draw near to each other 

 (Fig. 50, e) and fuse into a single 

 nucleus (Fig. 50, /, g, h). Next the 



zygote ends its fusion; instead of its original dumb-bell appearance, it 

 assumes the form of an oval cell, then grows large (Fig. 50, i). Occa- 

 sionally, however, it retains a vestige of the individuality of the two 

 gametes, showing two swellings joined by a somewhat narrower middle 

 portion (Fig. 50, ;). 



During this time, the cell becomes filled with little vacuoles and 

 assumes a more or less alveolar structure. 

 These vacuoles contain a number of metachro- 

 matic corpuscles. The nucleus which occupies 

 the center of the zygote begins to divide. The 

 ascus, containing sometimes four, sometimes 

 eight ascospores (Fig. 50,7), will then undergo 

 two or three successive divisions, as the case 

 may be. These divisions are accomplished by 

 karyokinesis or mitosis. In the stages preceding 

 nuclear division, the nucleus is very large and 

 shows a very clear structure with a nucleolus 

 and a chromatic reticulum (Fig. 51, a). It 

 soon elongates and assumes a special structure. 

 Its membrane loses its clearness, and in the midst of the nucleoplasm 

 an achromatic spindle appears, ending at each of its two poles in a 

 very small centrosome and containing at its center a group of fine 

 granulations representing the equatorial plate (Fig. 51, b and c). The 



FIG. 5 1 . Schizosac- 

 charomyces octosporus. 

 Various stages of the 

 nuclear division during 

 sporulation. 



