316 M. D. HILL. 
Association for kindly allowing me the use of their table, and 
to the officials of the station, by whom I was treated with all 
possible friendliness. 
The form I chose to work upon was Spherechinus granu- 
laris, which is exceedingly abundant at Naples, and could always 
be had in any number. Mr. Wilson studied Toxopneustes 
variegatus, while Mr. Matthews divided his attention between 
Asterias Forbesii andArbacia punctulata. With regard 
to Wilson’s interesting observations on the polarity of the egg 
and the axial relations of the two pronuclei, I am not in a 
position either to corroborate or refute his statements, my 
attention having been almost entirely directed to the behaviour 
of the centrosomes. I will therefore pass over the first part 
of his paper, which has to do with the living egg, without 
further comment, The result of his and Mr. Matthews’ study 
of series of sections of the eggs of the different forms they 
worked upon are summed up in the following words :—“ After 
the formation of the second polar body the egg archoplasm soon 
disappears, and no egg centrum, or egg archoplasm (‘ ovocentre’ 
as opposed to ‘spermcentre’) can be discovered at any subse- 
quent period. There is nothing like a quadrille to be seen save 
in doubly fertilised eggs (‘Toxopneustes). The archoplasm of the 
first cleavage-amphiaster is developed entirely from, or under 
the influence of the sperm archoplasm (‘spermocentre’ of Fol), 
and this is derived not from the apex of the spermatozoon, but 
from its base, undoubtedly from the middle piece (Toxopneustes 
Arbacia). . . . There is no centrum save as an artefact.” 
With regard to all but the last sentence, my results are 
practically the same as Wilson’s. In as far, therefore, as my work 
agrees with his, I shall deal very shortly with the facts, dwelling 
in greater detail on those points where our results differ. 
Method.—At once after the fertilisation of a great number 
of ova certain quantities were preserved, in a mixture of 
corrosive sublimate and acetic acid, at intervals of about five 
minutes, until the first cleavage-plane made its appearance. 
This usually took place about one and a half hours after fertilisa- 
tion, but the time varied greatly with the temperature of the 
