MATURATION OF UNFERTILISED EGG IN TENTHREDINIDA. 579 
very early stages to those of Rhodites, in which Henking 
concludes that there is no reduction (6, p. 156). 
My observations on centrosomes require a word of comment. 
In no case could I find centrosomes in the maturation spindles, 
but in all the species of which good preparations of the later 
stages were obtained they were easily seen in the segmenta- 
tion divisions (Pl. 36, figs. 31, 32). Since the eggs were 
unfertilised they cannot be derived from the spermatozoon, 
and it is certain, therefore, that they are produced from the 
ege-nucleus itself. Jenkinson (7, pp. 429, 449) concludes 
that in the Axolotl the centrosome arises by precipitation of 
the egg-cytoplasm under the influence of the sperm-nucleus, 
and mentions other cases of the same kind. Wilson (13, 
p. 566) observed that centrosomes arose de novo in par- 
thenogenetic eggs of Kchinoderms, so that when all these 
observations are taken together it may be taken as proved 
that the statement so commonly made that the centrosome is 
derived from the middle piece of the spermatozoon is at least 
not universally true. 
The centrosomes found in eggs of impregnated females of 
N. ribesii do not differ in any respect from those seen in 
virgin eggs. 
10. Summary AND Discussion or Resutts. 
The chief facts described are as follows : 
(1) In all the species investigated the first maturation 
spindle is found on the dorsal surface of the egg, in a little 
patch of protoplasm not far behind the anterior end. ‘I'he 
first polar mitosis is never completed, for, at the end of the 
anaphase, a new spindle is formed at each end, and the second 
polar mitosis begins. 
(2) The second maturation division gives rise to four nuclei 
lying in a line perpendicular to the edge of the egg; of these 
the innermost is the female pronucleus or egg-nucleus, the 
next is that of the second polar body, and the two outer are 
the daughter-nuclei of the first polar body. 
