HIRUDJNEA. 
Verm. 35 
of each side (i) forms the nerve-cord, the three lateral series (ii-iv) forni 
the circular muscles, and have nothing to do with the formation of the 
nephridia, which arise in the inner mesodermic layer. In Aulastoma the 
primitive epidermis becomes thrown off, and the definitive epidermis 
arises from the three lateral series ,(ii-iv). The cells of these rows 
undergo oblique division, and in this way the products of division come 
to lie between the outer layer of the germ-band ( i.e ., the future epidermis) 
and the inner mesoderm-plates. These deeper-lying cells give rise to the 
circular muscles. The nervous system arises as in Clepsine , and appears 
for a time as a groove, which then flattens out. In addition to the cells 
of the neural series (i), certain cells of the primitive nerve-plexus take 
part in the formation of the definitive nerve-chain. Author concludes 
that the Hirudinea are very closely related to the Oligochceta, and that all 
resemblances which they show in their structure to the flat worms are 
merely analogies, and not homologies. 
Bolsius (2) gives a description of the ciliated organs of Nephelis , 
discovered by Yon Siebold in 1848. Hitherto the ciliated organs of 
Nephelis have been considered as the coelomic funnels of the nephridia ; 
but, as a matter of fact, they are quite distinct from the nephridia and 
without any relations to them. They are suspended by bands of con- 
nective tissue in capsules, the cavities of which belong to the botryoidal 
system of Bourne, and which are separated from the segmental organs by 
muscular and connective tissue. While thus being morphologically 
equivalent to the nephridial funnels of the Chcetopoda , they are physio- 
logically quite different. Author has found that the cavity of the 
ciliatod organ is usually fillod with small loose colls like blood-corpusclos. 
He therefore suggests two alternative hypotheses as to the function of 
the ciliated organs, viz. : they may serve to keep the blood in motion in 
the non-contractile botryoidal system ; or, they are the points from 
which the production of blood-corpuscles takes place. 
Burger (1) finds that in the larva of Nephelis the coelom appears as a 
series of separate paired segmental cavities, formed by a splitting of the 
two inner layers of the germinal band. They then communicate on each 
side with an unsegmented median cavity, which arose in the same way as 
the side cavities, but subsequent to them, and which extends along the 
whole length of the germinal band. Its lumen is much greater than that 
of the side-cavities. 
In consequence of the presence of the median cavity, a ventral mesen- 
terium is not formed, as it is in the Annelids. Similarly, the segmental 
cavities never extend so far dorsally as to form a dorsal mesentery, 
owing to the rapid formation of mesenchym at the dorsally directed 
region of the somites. In Nephelis the septa between the somites, which 
are at first thin membranes, increase enormously in bulk by rapid cell- 
division and form massive walls, and so in great part usurp the cavities 
of the somites. The tissue which is thus formed consists of a gelatinous 
substance, in which are scattered numerous large spherical cells. The 
point of origin of this mesenchym is situated in two prominent longi- 
