qe M. D. HILL. 
two, although the corresponding division of the astrosphere 
itself does not take place till somewhat later. As Boveri (2) has 
described and figured for Ciona intestinalis, the astrosphere 
lengthens out,— the rays contracting somewhat,—becomes dumb- 
bell-shaped, and finally constricted off in the middle into two 
separate spheres. In Phallusia, however, the pronuclei fuse 
somewhat differently, as will be seen by comparing fig. 18 with 
fig. 29 in Boveri’s paper (2). The two astrospheres and also 
the two nuclei are at this stage very difficult to stain, and this 
may account for the fact that from this until the Amphiaster 
stage there was no trace of a centrosome to be found. The 
interior of the astropheres show,a reticular structure, which is 
maintained till the Amphiaster stage, when the centroscmes 
become visible again, and the network gives place to a clear 
“space,” or at most a slightly reticular central mass (figs, 
17 and 18). 
Tn the first cleavage-spindle I have counted from thirteen 
to sixteen chromosomes, and on theoretical grounds it is neces- 
sary to assume that the latter is the correct number, which 
would give eight derived from the female, and eight from the 
male pronucleus respectively. I do not wish, however, to lay 
too much stress on the exactitude of these numbers, though I 
believe they are approximately correct (fig. 19). 
With regard to the conditions of the chromatin in the 
development of the spermatozoa, it was only possible to sub- 
stantiate the fact that one spermatocyte I.gives rise to two 
spermatocytes II, and these again each divide into two, form- 
ing in all four spermatids. Further, the two nuclear divisions 
take place without any intermediate resting phase. Beyond 
this, however, nothing could be definitely ascertained as to the 
number of the chromosomes in any stage of development, 
owing to the extreme minuteness of the cells themselves. 
It may be interesting to note that the ova of certain 
specimens, which had been kept in the aquarium tanks for a 
long time, were found to be infested with long rod-like bodies 
seemingly of a bacillic nature. Although these ova were 
mixed with ripe sperm, no single fertilisation ever took place, 
