SOME PROBLEMS OF REPRODUCTION. 63 
(e) The non-utilisation of all the cytoplasm in the elabora- 
tion of the flagellate (or ciliate) spermatozoon from a tissue- 
like cell, leaving a non nucleated residuum (higher Cryptogams 
and some Animals). 
(f) The leaving over of a central portion of cytoplasm, as a 
non-nucleate blastophore, in the modified sperm morula, 
where budding replaces true segmentation (Lumbricus, 
Metazoa, &c.). 
(g) The differentiation of the basal cell of one of the earlier 
stages of the fission of an attached spermatogonium as a 
nucleated blastophore (Helix and some Vertebrates ; it is 
the first daughter-cell of the spermatogonium in Sponges). 
(4) The abortion of some of the spermatogonial or oogonial 
cells (Ascaris). 
(i) The abortion of some of the gametes of a brood as 
“polar bodies” in the Metazoa, owing to one appropriating 
the greater part of the cytoplasm. 
(k) The abortion of some of the gametonuclei, with or with- 
out a minimal quantity of cytoplasm, as rejection-nuclei 
(Ciliate Infusoria and some Fucacez). 
(1) The degradation of some of the oogametes or progametes 
of a brood to serve as transmitting media for the spermatozoon 
(canal-cells of Archegoniates and Gymnosperms). 
(m) The retention of numerous gametonuclei in the peri- 
pheral part of the apocytial cytoplasm, which is destined to 
form an outer investment around a single central gamete 
when transformed into the zygote (Peronosporee and 
Ophryocystis?). 
(n) The first formation of sterile cells in the pollen grain of 
Gymnosperms, and of a vegetative nucleus in those of Angio- 
sperms representing the formation of a vegetative prothailus, 
and having no real connection with the subsequent gameto- 
genic divisions of the other or sexual nucleus. 
(0) The non-utilisation of some of the gametonuclei formed 
in the pollen-tube of the Siphonogamous Metaphytes, and 
the antheridium of Peronospora.! 
1 This case finds a close parallel in the formation of the innumerable sper- 
