DEVELOPMENT OF THE GENERATIVE ORGANS. 695 
in diameter. Their nuclei vary in size from I to 24 in 
diameter. They are arranged in rows very regularly, and 
the rows are frequently seen to radiate from the centres of 
the polyblasts. There is no indication of the division of the 
cell substance between these nuclei. 
Lee has certainly observed the formation of the polyblasts 
by the repeated division of the nuclei of the spermatospores 
in Sagitta, and his figures leave no doubt upon the question in 
my mind, although he says in his text, ‘I have been unable to 
follow the genesis of these polyblasts.’ 
From this stage onwards there is no conformity in my obser- 
vations and those of Lee; this is undoubtedly due to the fact 
that the formation of the spermatozoa takes place somewhat 
differently in the Chetognatha and the Muscide. 
The Spermatozoa are formed in packets, each packet corre- 
sponding to a polyblast. The polyblasts become pyriform, 
with the thick end towards the surface of the testicle, and all 
the nuclei are arranged near this thick convex end. The 
polyblasts then split up into a number of fusiform segments. 
These are the young spermatozoa; each at this stage exhibits 
a distinct vesicular nucleus. 
All my best preparations are stained with picrocarmine and 
the nuclecli of the young spermatozoa are most definitely 
stained, whilst the cell substance is sufficiently coloured to 
render it very distinct. In such preparations there is no trace 
of a secondary nucleus (Nebenkern). 
The succeeding stages are very simple: the nuclei cease 
to exhibit a distinct vesicular character, and their size is 
less than that of the nuclei in the young spermatozoa. The 
nuclear vesicle has evidently disappeared, leaving only a small 
ball of chromatin surrounded by a thin layer of protoplasm, 
which is continuous with the tail. The tails increase rapidly 
in length, so that they not only extend across the whole 
diameter of the testis, but are frequently curved ; at the same 
time they acquire the property of staining deeply, and exhibit 
a distinct yellow tinge, owing to the action of the picric acid. 
The size of the bundles of spermatozoa varies considerably, 
