451 
GENESIS, OR PARTHENOGENESIS. 
Up to this period the preparation of generative organs has pre- 
ceded the formation of the embryo which is to possess them. 
It will be remembered that this is distinctly expressed in the 
extract given above from Owen’s account. The peculiarity, 
indeed, of Balbiani’s discovery consists in his demonstration 
of the male organ, and the seminal corpuscles of its seminal 
reservoir, as also the communication by ducts with the ovarian 
tubes. 
According to Balbiani, the development of the embryo 
commences by the proliferation of blastoderm cells from the 
edges of the gap formed by the rupture of the blastoderm 
envelope. From the margin of this gap a layer of blastoderm 
grows inwardly, applying itself against the inner surface of 
the general blastodermic envelope, then folding upon itself 
turns back again towards the gap. This curved lamina is 
the embryonic rudiment of the cephalothoracic and abdo- 
minal portion of the embryo. From the lower edge of 
the gap grows a mass of blastoderm, which forms the head of 
the embryo. The first-mentioned rudiment of the embryo 
(the primitive streak) becomes furrowed, and on each side the 
longitudinal halves quickly develope as germinal tuberosities. 
In proportion as the primitive streak penetrates into the interior 
of the ovum the sexual masses previously described follow it 
in its movement, and place themselves against the inner 
face of the upper reflected abdominal portion, though still 
outside the embryo, the abdominal cavity not being yet closed 
in. The development proceeds until the mouth and anus, with 
the two ends of the digestive tube, are visible. Then occurs 
a curious change of position, described as a backward summer- 
sault of the embryo in the interior of its capsule. The capsule 
here spoken of is the original blastodermic envelope, which, 
except at the points from which the embryonal blastoderm 
sprang, has ceased to grow, but is transformed into a 
delicate membrane, enveloping the embryo in a sort of sac, 
which isolates it from the ovarian chamber. 
From the alteration of position the head arrives at the 
opposite end of the capsule, the ventral surface first curved 
inwards now curves outwards, the abdomen is transferred to 
the dorsal side and rises up towards the head. The space left 
between the abdominal and cephalothoracic segments is now 
occupied by the masses of the generative organs. By the 
growth of the ventral arch towards the dorsal region, and the 
fusion of its sides in the median line, the closure of the hinder 
part of the body is effected. 
The female ovules, with their surrounding cells, each forming 
a separate small mass enclosed in its proper envelope, are now 
seen symmetrically placed in two groups in the posterior part 
