594. ARTHUR THOMSON, 
(2) The elements extruded at a later stage, the ‘‘ globules 
tardifs,” result in the granular cells of Ascidians, probably too 
in the globules of the shells of winter eggs of Cladocera 
(Weismann), in the curious envelope of the ova of Chiton 
(Hering), in the peripheral hyaline bodies on the eggs of 
Phanerocarpous meduse (Giard). Giard has observed 
(‘Comptes rendus,’ March, 1877) the extrusion of hyaline 
globules all round the periphery of Rhizostomum, &c. 
(3 a) He notes also some difficult cases of globules expressed 
at maturity but without karyokinetic change of the nucleus, 
e.g. the “voile”? in the ova of certain Amphibians, first 
observed by Max Schultze (1863) and termed fovea germi- 
nativa, and since investigated by Bambeke and O. Hertwig. 
With these it is interesting to compare the yolk globules recently 
(‘ Archiv f. mikr. Anat.,’ xxvi, December, 1885) demonstrated 
by Solger on the intracapsular space of certain fish ova. 
Mode of Formation.—The classic researches of Fol and 
Hertwig as to formation of polar cells have been generally con- 
firmed. Van Beneden, however, maintains that in Ascaris 
megalocephala the division takes place parallel to the 
long axis of the nuclear spindle, so that two dissimilar halves 
might result. His results have been ably summarised in a 
recent number of this Journal. Sabatier agrees with Van 
Beneden as to the longitudinal division, and maintaining that 
the extrusion is not directly comparable with ordinary indirect 
cell-division, asserts the concurrence of two distinct processes, 
not necessarily related, (1) the formation of a nuclear spindle 
aud consequent division, and (2) the independent expulsion of 
a more or less considerable mass of circumnuclear protoplasm. 
As to the further history of the polar cells, it has been observed 
by Trinchese and others that they sometimes divide each into 
two and then into four cells. Flemming (‘ Biol. Centlblt.,’ iii, 
21, 84) has pointed out the constancy with which, in some 
cases at least, the polar cells appear at a definite position on 
the ovum, e. g. in Anodonta the polar cells appear constantly 
antipodal to the “ haft-pole,” at which the ovum is attached 
to the membrane. 
