SEX DETERMINATION IN DINOPHILUS GYROCILIATUS. 361 
regard to the peculiar form of fertilisation described in the fore- 
going part of this paper. In the following section the facts with 
regard to the maturation divisions are briefly stated, as far as 
I have been able to determine them up to the present, their 
full consideration being left for a future paper. 
Korschelt (6) and Yon Malsen (8) have established that in 
D. apatris the male and female eggs each give off two polar 
bodies, and this is also the case in D. gy rocili at u s, as I 
have mentioned. The first polar body in both the male and 
female eggs divides again, therefore in the polar furrow of 
the first segmentation division three polar bodies are seen. 
They are extruded as soon as the eggs come in contact with 
the sea-water, and, as in D. conklinii, are absorbed during* 
segmentation by one of the blastomeres. 
(a) In the Male Egg. 
In fig. 41 is shown a polar view of the first maturation 
spindle in the male egg. Twenty chromosomes are shown — 
the full somatic number. Twenty go out, and twenty remain 
in the egg (fig. 39). 
In the second polar body in the male apparently ten double 
or dumb-bell shaped chromosomes go out and the same num- 
ber remain in. In the first segmentation division of the male 
egg the full somatic number, twenty, is shown again (fig*. 46). 
The full somatic number seems to be established through the 
breaking down of the ten double chromosomes remaining in 
the egg after the second maturation division (fig. 43). Each 
of these ten chromosomes breaks down into a special nucleus, 
and in a stage like that shown in fig. 43 each of the small 
nuclei contains two chromosomes. 
In the maturation stages of the male egg a peculiar body 
is more or less constantly present (figs. 38, 39, and 45, pr. b.). 
This structure seems to have nothing to do with the process 
of maturation, and would seem to correspond with the so- 
called “ besondere ” body of many investigators. It usually 
presents the appearance of a dark, irregularly staining body 
