84 SYNGAMY IX PKOTOZOA 



macrogametes. Sometimes this occurs before the oocyst has formed; at 

 other times after its formation, in which case a pore, the micropyle, is 

 present at one end of the cyst, and through it the microgamete makes its 

 way. The microgamete enters the cytoplasm of the macrogamete, which 

 immediately commences to secrete a substance which closes the micropyle. 

 Though several microgametes may be attracted towards one macro- 

 gamete, immediately one has entered its cytoplasm this attraction ceases. 

 The nucleus of the. macrogamete has meanwhile been drawn out into a 

 long spindle, the fertilization spindle, on the fibres of which the chromatin 

 granules are distributed. The microgamete nucleus breaks up into 

 granules, which gradually become distributed upon the fertilization 

 spindle. The spindle now retracts, and a spherical nucleus containing 

 chromatin from both the macrogamete and microgamete is again formed 

 (Fig. 337). 



Amongst the pigmented blood parasites of the genera Plasmodium 

 and Hcemojjroteus a similar type of union occurs. The nucleus of the 

 macrogamete moves towards the surface of the body, which is raised up 

 at this point into a small elevation. The elongate motile microgamete 

 enters this elevation, and its nucleus unites with that of the macrogamete 

 (Figs. 383 and 391). 



Amongst the Euciliata, when conjugation occurs amongst free-swim- 

 ming forms, it is usually by the peristomes that they become attached 

 to one another. Actual continuity of cytoplasm appears to take place 

 just behind the peristomes, to allow of the interchange of nuclei, as 

 described above. In the attached forms, such as Vorticella, conjugation, 

 as already noted, takes place between a large attached individual and 

 a small free-swimming ciliated form which has been budded of! from 

 another individual. The small free-swimming form attaches itself to the 

 larger one at a point near the insertion of its stalk, and wdien exchange 

 of gamete nuclei has occurred it degenerates (Fig. 44). 



METHOD OF FORMATION OF GAMETES.— The actual method by which 

 gametes are formed from gametocytes varies to some extent. Amongst 

 the gregarines, the nucleus of the gametocyte multiplies by a series 

 of divisions till the requisite number of nuclei are present (Fig. 465). 

 These are then arranged upon the surface of the gametocyte, and little 

 elevations of the cytoplasm are formed. Into each of these there passes 

 a nucleus. Each small cytoplasmic elevation or l)ud, which has acquired 

 the characteristic form of the gamete, is now separated by a constriction. 

 A large amount of the cytoplasm is usually left over as a residual body. 

 In the case of the coccidia and allied forms, where there is an extreme 

 condition of anisogamy, one gametocyte, the macrogametocyte, gives rise 

 to a single macrogamete. It is supposed that this transformation takes 



