86 SUMMARY OF CURRENT RESEARCHES RELATING TO 



and probably spheres, " the final stage of intracellular multiplication." 

 In quite young rats he found all stages of forms dividing by equal and 

 unequal fission ; forms with a very long posterior end ; irregular types 

 with three or four miclei, three or four centrosomes, and three or four 

 flagella. 



Herpetomonads in Mice.*— H. B. Fantham and Annie Porter have 

 found herpetomonads (or leptomonads) in mice. They are led to the 

 conclusion that the origin of the infection is to be sought in a flagellate 

 of an ectoparasite of the mouse. This flagellate is very probably 

 Herpetomonas pattoiii. a natural or specific parasite of fleas (especially 

 rat-fleas), which can adapt itself to life in the blood of mice. Herpeto- 

 monads have been recorded from rat-fleas, dog-fleas, and human-fleas. 

 It is probable that the flagellates are varieties of one species, H. pattoni, 

 which can live in the l)lood and certain internal organs of rats, mice, 

 dogs and man. 



'o 



Chromosome Cycle in Coccidia and Greg-arines-t-Clittord Dobell 

 and A. Pringle Jameson have studied, respectively, the coccidian Aggre- 

 gata eherthi Labbe and the gregarine Dijilocystis schiieiderl Kunstler. 

 Their investigation of these two organisms has shown that the nuclear 

 divisions at all stages in the life-histories are mitotic, and that the 

 chromosome numbers are remarkably constant. 



In A. eberthi the chromo.somes are six in number at everv nuclear 

 division in the life-history with one exception. This is the division of 

 the zygote nucleus immediately succeeiling fertilization. There are 

 here twelve chromosomes, which become halved to six in the course of 

 this division. Reduction thus occurs immediately after fertilization — 

 not during gametogenesis. The six chromosomes must be regarded as 

 representing the haploid number— the diploid nnml)er (twelve) being 

 present in the zygote nucleus only, while its division is a reduction 

 division. Since the haploid num])er (6j occurs in both the sexual and 

 the asexual cycle, there is thus no differentiation in respect of chromo- 

 some number in the two generations. 



In D. schneideri the number of chromosomes in all the nuclear 

 divisions is, with one exception , three. At the first mitosis in the spore, 

 six chromosomes are formed by the segmentation of the spireme thread. 

 These separate into two homologous groups of three each, which repre- 

 sent the two sets of chromosomes derived from the two gamete nuclei 

 which united to form the nucleus of the zygote. This first division 

 in the spore — immediately following fertilization — must, therefore, be 

 regarded as a reduction division. The haploid number of chromosomes 

 is three, and occurs in all the nuclear divisions of the gamont, and in 

 all the spore divisions except the first. The diploid number is six, and 

 is found at only one division in the whole hfe-cycle — the first sporal 

 division, immediately following fertilization. Reduction thus occurs 

 directly after fertilization, and not during gametogenesis. 



*' It is clear that the chromosome cycle of Aggreyata agrees, in 



* Parasitolcgv, viii. (1915) pp. 128-32 (7 figs.). 



t Prcc. Roy. Sec, Series B, Ixxxix. (1915) pp. 83-94 (2 figs.). 



