ON FECUNDATION, MATURATION, AND FERTILISATION. 323 
That they were not, however, quite destitute of vitality is 
shown by the fact that polar-spindles were formed, although of 
an apparently pathological nature (fig. 20). 
For the structures needing high powers of the microscope, 
Zeiss’s apochromatic 2:0 mm., apert. 1°30, homogen. immers. 
was used with compensating ocular No. 8, and an Abbé 
condenser. 
SUMMARY AND CONCLUSION. 
The above results may be shortly summarised as follows: 
(1) InSpherechinus granularis and Phallusia mam- 
millata there is no egg astrosphere or egg centrosome. Both 
these structures are brought into the ovum by the spermatozoon, 
and they give rise by division to all the subsequent astrospheres 
and centrosomes throughout ontogeny. There is, consequently, 
no such thing as a “ quadrille.”’ 
(2) In both forms the sperm head rotates through 180°, and 
the astrophere and centrosome are elaborated out of or under 
the influence of the middle piece. 
(3) In Phallusia the nucleus of the ovocyte I-contains eight 
chromosomes irregularly dispersed throughout its substance. 
(4) In the two succeeding nuclear divisions these eight 
chromosomes divide into sixteen each time, eight passing out 
into the first and eight into the second polar body. There is 
consequently no equalling or “reducing division” at this 
period. 
(5) The sperm head breaks off into eight chromosomes, and 
sixteen are found in the first segmentation spindle. 
The origin and fate both of astrospheres and centrosomes in 
Spherechinus and Phallusia certainly tend to support Boveri’s 
generalisation, that the ovum when ready for fertilisation 
possesses two out of the three essentials for cell division, viz. 
cytoplasm and nucleoplasm, but is without the third, or 
centrosome; while, on the other hand, the ripe fspermatozoon 
possess nucleoplasm and centrosome, but little or no cytoplasm. 
It is therefore only when the union of the male and female cells 
takes place that the requisite conditions for development are 
