100 W. M. Smallwood 
know only by a similar metamorphosis in Haminea. As the ma- 
turation figure becomes radial in position and of a length approxi- 
mating the second figure, the spindle formed from the two centrioles 
breaks away and is lost in the cytoplasm. The two asters now 
separate, the deeper one moving nearly to the centre of the egg. 
A new spindle must be formed from the eytoplasm. The first ap- 
pearance of these new fibres is a linear arrangement of granules 
which become fused into a single fibre (Fig. 12). These continue 
to form in a similar manner until a new spindle appears (Figs. 13 
and 14). Although the old astral rays remain, new ones are formed 
in the same way that the spindle fibres arise. The full details of 
this unusual process are presented in my paper on Haminea (Figs. 46 
—51). The conditions are the same in Doris and Haminea in all 
of the changes except one. This exception in Haminea consists in 
the formation of unmistakable fibres proceeding from the centro- 
somes while they are still enclosed in a vesicle; these are rays 
which are in addition to the ones formed from the eytoplasm. No 
such process was discovered in the growth of this new spindle in 
Doris. 
Fertilization. Although it was not the purpose of this paper 
to make a detailed study of fertilization yet the following facts 
were noted while observing the maturation phenomena. The sperm 
head penetrates the ovum in the oviduct just before deposition. The 
tail of the sperm is left outside. As soon as the head has entered 
the egg, it inereases in size and is usually slightly bent near the 
middle. A few small granules elose to the sperm head stain more 
intensely than the rest of the eytoplasmie granules but I was not 
able to determine their origin. The sperm head moves across the 
egg toward the animal pole, its path depending on the place where 
it entered the egg. In this approach to the animal pole the sperm 
nucleus becomes vesiceular in the usual manner. But while passing 
through these changes, the chromatin may be confined in one vesicle 
(Fig. 18) or several (Figs. 15, 17, 21). In most cases there is one 
quite large vesicle and a few small ones. The large one eventually 
absorbing the others. Structurally there is no essential difference 
between these different vesicles aside from their size. In Fig. 17. 
the two small sperm vesicles, each containing a bit of chromatin, 
have the same appearance as those represented in Figs. 9—10, 
These sperm vesieles seem to be derived from the eytoplasm forming 
under the influence of the chromatin. When the chromatin remains 
