336 
CRESSWELL SHEARER. 
is probable that some other division takes place in the case of 
the female egg. This ratio, however, varies widely, as the 
table in the following' section will show, and according to 
Yon Malsen ( 8 ), it can be greatly altered by conditions of 
heat and cold. I have been unable to obtain any light 
on the subject from my sections. It is impossible to follow 
the above described cytological changes on living material. 
2. Material, Habits, Methods, etc. 
The group of primitive Annelids, represented in the genus 
Dinophilus, comprises some eight or nine species. They 
are remarkable for the fact that some show a well-marked 
sexual dimorphism, in which the male is rudimentary, 
without any mouth or digestive tract, while in others the 
sexes are the same size and exhibit no signs of this 
dimorphism. The group as a class, therefore, is readily 
divisible into two subdivisions, in one of which all the 
species are sexually dimorphic and unpigmented, while in the 
other they are an orange red in colour, and sexually mono- 
morpliic. The former may be called the Leucodinophilidae, 
while the latter may be called the Erythrodinophilidae. The 
known species, many of which are of doubtful specific value, 
may be arranged under these two subdivisions, as follows : 
Leucodino- 
philidae 
1. Dinophilus gy rociliatus, Schmidt, 1857- 
2. 
33 
apatris, Korschelt, 1882. 
3. 
33 
conklinii. Nelson, 1907. 
4. 
33 
metamero ides, Hallez, 1879. 
5. 
33 
pygmaeus, Verrill, 1892. 
Erythro- 
dinophilidae 
6 . 
7. 
8 . 
9. 
jf 
33 
33 
33 
vorticoides, Schmidt, 1848. 
gardineri, Moore, 1899. 
toeniatus, Harmer, 1889. 
gigas, Weldon, 1886. 
Of the Leucodinophilidae the first three species, D. gy ro- 
ciliatus, D. apatris, D. conklinii, are closely related, 
