THE DEVELOPMENT OF ALCYON1UM DIG! TATUM. 
61- 
interval between the end of this stage and the subsequent 
formation of definite lobes, and again between the protrusion 
of lobes and the actual production of blastomeres was also 
very variable. Before segmentation begins the surface of 
the egg usually becomes pushed out into eight equal or 
unequal lobes (Text-fig. 27). However, sixteen lobes are 
sometimes protruded instead of eight (Text-fig. 28). In one 
such case the first lobe slowly formed about two hours after 
fertilisation, and soon afterwards the second, third, and fourth 
lobes followed, all at one pole (Text-fig. 29, l.). Next larger 
lobes slowly formed towards the opposite pole (Text-fig. 29, L.), 
and while these increased in number all the lobes became 
more prominent. Two and a half hours after fertilisation 
the lobes were still increasing in number, and half an hour 
later still sixteen were counted embracing the whole surface 
of the egg. Sections of this stage revealed one nucleus only,, 
but in sections of other similar embryos the nucleus was 
rapidly dividing into daughter nuclei. When only eight lobes 
form they are necessarily larger in size than when sixteen 
are protruded (cf. Text-figs. 27 and 28). Great variability, 
however, exists in the protrusion of lobes ; many eggs seem 
to throw them out in a very irregular manner, the lobes 
themselves varying in number: thirty-two, sixty -four, and 
other numbers have been counted. 
In the majority of ova, while eight equal or unequal super- 
ficial lobes are protruded, the centre yolk remains at first 
undivided (PI. 3, fig. 8, C.'M.). Subsequently the grooves- 
between the . lobes deepen, extending towards the centre of 
the egg, and almost cutting it into eight segments. Finally 
the segments become rounded off from one another at the 
centre, leaving a little granular protoplasmic waste in the 
newly formed segmentation cavity (Text-fig. .30, and PL 3,. 
fig. 9, S. C.). This cavity persists until the end of the morula 
stage. Usually the oosperm nucleus is found lying near the 
region where the first lobes form, and, though it may divide 
up into eight daughter nuclei while the lobes are being pro- 
truded, the fission of the oosperm nucleus is sometimes- 
