188 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
pieces. It was lively and vigorous. Similar cases have been recorded 
by Leidy and Warren Knaus. 
Maturation and Fertilisation in Opliryotrocha puerilis.* — Dr. E. 
Korschelt comes to the following conclusions : — The division of the 
spermatogonia and oogonia is mitotic. Amitotic nuclear divisions occur 
in the intestinal epithelium, though karyokinetic figures are also ob- 
served. The number of chromosomes in dividing cells is four, but some 
of the later cleavage cells may show eight chromosomes in each daughter- 
plate. As the blastomere nuclei prepare to divide, the nuclear frame- 
work disappears, but it reappears after the dissolution of the nucleolus. 
The nuclei of the nutritive ceils and of the oogonia or oocytes are at 
first alike, but the former acquire a dense nuclear framework, a dark 
colour, and irregular shape, while in the latter the sparse nuclear frame- 
work forms nuclear threads. 
The four chromosomes in the germinal vesicle are at first long 
loops ; they soon shorten and split longitudinally, appearing as four 
split rods. A granular, slightly stainable, viscid substance perhaps 
helps in forming the spindle fibres, which appear within the nucleus, 
while the membrane is still quite intact. The centrosome, with its rays, 
is first seen near but outside the nucleus ; it soon divides, with a sort of 
transient central spindle. The chromosomes become disposed in the 
middle of the nucleus, the spindle fibres become more distinct, the 
membrane disappears, and a plump, barrel-shaped, first-directive spindle 
is formed. 
The four rods lie in pairs, one behind the other, and the longitudinal 
cleavage disappears. The spindle becomes very long and narrow, the 
four closely juxtaposed rods occupy little room, the mantle fibres run 
from pole to pole, there is no central spindle. 
In forming the first polar body the spindle moves to the margin, the 
four chromosomes separate in pairs, the longitudinal cleavage is again 
distinct, and four chromatin grains are given off. From the internal 
daughter-plate is formed at once the equatorial plate of the second 
directive spindle ; the chromatin bodies again diverge in pairs, and two 
pass out into the second polar body. 
Both polar bodies are distinct cells ; the first may again divide by 
karyokinesis. Instead of granular chromosomes, chromatin loops may 
occur. The splitting of the chromosomes of the first directive spindle 
may be suppressed, and the first polar body may thus have two entire 
chromosomes. In other cases the splitting occurs earlier than usual, so 
that the first directive spindle, still uncontracted, may show, in the 
middle of the ovum, eight chromatin granules. The formation of the 
first polar body is clearly a reducing division. 
Fertilisation is external, soon after egg-laying. Polyspermy results 
in abnormalities. Around the spermatozoon which has penetrated the 
ovum, a radiate system develops, and a centrosome appears to arise from 
the middle portion. Centrosome and ray-svstem divide. The centro- 
somes of the first segmentation spindle are both formed from the 
spermatozoon. 
The two pronuclei are at first irregular, but become rounded. Their 
* Zeitschr. f. wiss. Zool., Ix. (1895) pp. 543- G88 (7 pis.). 
