1904. | NATURAL SCIENCES OF PHILADELPHIA. ar7 
spherical or ovoid bodies having a lower part full of transparent 
liquid, in which lay concretions of a yellowish color. These he denomi- 
nated ‘‘nephrocisti’”’ (nephrocysts) and ascribed to them a mesodermal 
origin, since they have no connection with the exterior. Haddon 
(1882) found a mass of cells on the right side of Jantheria and Philine, 
near the anus in Elysia on the left side, and in Pleurobranchidium on 
both sides. In 1888 Rho found similar organs in Chromodoris which 
he stated arise from a few mesoderm cells containing numerous con- 
eretions and excreta which indicate their functional value. He con- 
cluded that this structure corresponds to the right Prosobranch 
kidney, considering the left to be rudimentary. Lacaze-Duthiers 
and Pruvot (1887), in a paper on Opisthobranch embryology, described 
the anal organ of Aplysia, Philine, Bulla, Pleurobranchus, Doris and 
members of the family Aolidide, stating that in origin it is entirely 
ectodermal and that it was none other than an “analeye.’’ This eye, 
it was claimed, becomes strongly developed in the blind !arve and 
later atrophies as true eyes appear. It stands in connection with a 
cell-mass, ganglionic in nature, the ‘asymmetrical centrum”’ of 
Lacaze-Duthiers. 
Mazzarelli (1892) came to some very different conclusions from work 
on Aplysia. He believes the organ in question to have neither the 
structure nor function of an eye, and, moreover, it remains present 
in the larve after eyes are developed. From its position and structure 
it is doubtless a kidney. He derives it from paired rudiments which 
originally were closely associated with the endodermal elements of 
the aboral pole (mesentodermal cells) and which later, separating, 
wander into the blastocoel cavity and, after torsion begins, first the 
left and then the right come to lie in the neighborhood of the anus and 
together form a small cavity which acquires communication with the 
exterior. This unpaired kidney is homologous to the kidney (‘‘niere”’) 
which in many Prosobranchs is found in the same place and, as is 
well known, forms the anlage of the definitive kidney. Mazzarelli, 
therefore, concludes that the anal kidney of the Opisthobranch larva 
is a secondary kidney (‘‘secondare niere”’), while the primitive kidney 
of these Mollusks is already known (the “‘nephrocisti’”’ of Trinchese). 
The anal kidney is but the anlage of the definitive kidney, which in 
this case corresponds not to the right but to the left adult kidney of 
the Prosobranch. 
Heymons (1893) has carefully described the conditions found in 
Umbrella. The excretory rudiment is here at first paired and arises 
from the cells 3c", 3d", which sink somewhat below the surface and 
