470 
a heavy or very abundant one; and I have only seen three or four in- 
stances of the ordinary double infection. It is a remarkable fact, be- 
sides being of most unusual occurrence, that in such a number of cases 
two (and only two) small Halteridial individuals should have entered 
the same corpuscle close together, have undergone cytoplasmic union 
while young, and assumed just the same form and increased in size as 
an ordinary single gametocyte (of either sex), ultimately tending to 
separate as they become adult. I am unable to say, however, whether 
two such individuals would become, as a rule, fully mature. The great 
majority of these double parasites which I have seen are nothing like 
double the size of a ripe gametocyte (cf. figs. 13, 14), hence each half 
has not nearly attained the maximum size; the parasites of figs. 7 and 11 
have as large a bulk as any I have noticed. 
In conclusion, I should like to point that what appears to me to be 
a quite parallel state of affairs in Haemocystidium has been described 
and figured by Dobell!, though that author has regarded the condition 
as representing schizogony (in the small forms) or nuclear division (in 
the adult gametocytes). On the same grounds as those discussed above, 
I feel fairly certain that Dobell’s figures 14 and 16, pl. 7, of very large 
gametocytes of either sex, each with two nuclei, are really instances of 
a double infection of a corpuscle by gametocytes of the same sex, just 
as his figs. 17 and 18 show double infection of a corpuscle with game- 
tocytes of opposite sex. Dobell says that double infection of a cor- 
puscle is not uncommon, but apparently does not take into consideration 
the possibility that the two individuals in one corpuscle may be of the 
same sex; and there is no reason to suppose this cannot occur, just as 
readily as double infection with individuals of opposite sex. Now a 
corpuscle infected with two gametocytes of the same sex (either male 
or female), would present the same appearance as shown in Dobell’s 
figs. 16 and 14, respectively; and I have little doubt that is really the 
condition there represented. Similarly, with regard to the schizogony 
of small forms, which Dobell says is most usually of the nature of 
binary fission, I think it is much more probable that the author’s 
figures 4—7 should be read in the opposite direction, as indicating suc- 
cessive stages in the cytoplasmic union of two small individuals which 
have entered the same corpuscle; granted the occurrence of double in- 
fection, the two parasites must enter the cell as small forms. Dobell 
says the infection is often quite intense; this explains the occasional (in- 
frequent) occurrence of three or four small parasites in a corpuscle, 
which have united. In short, Dobell’s figures are quite comparable to my 
4 Festschrift R. Hertwigs. Bd. I. 1911. p. 123. pl. 7. 
