1904.] NATURAL SCIENCES OF PHILADELPHIA. 377 



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 

 oridn, 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 Elijsia 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- 

 cretions 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 Aplijsia, Philine, Bulla, Pleurobranchus, Doris and 

 members of the family ^olidida, stating that in origin it is entirely 

 ectodermal and that it was none other than an " anal eye." This eye, 

 it was claimed, becomes strongly developed in the blind larva and 

 later atrophies as true eyes appear. It stands in connection with a 

 cell-mass, ganghonic in nature, the "asymmetrical centrum" of 

 Lacaze-Duthiers. 



Mazzarein (1892) came to some very different conclusions from work 

 on Aplysia. He beUeves the organ in question to have neither the 

 structure nor function of an eye, and, moreover, it remains present 

 in the larvae 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^ al3oral 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 MoUusks 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 m 

 Umhrella. The excretory rudiment is here at first paired and arises 

 from the cells 3c^S 3d^\ which sink somewhat below the surface and 



