In some forms the kidney is closely associated with the gonad, and seems to coperate with the latter in the generative functions.
The gonad is the part most affected; so much so that most authors have interpreted it as testis.
In Arca, in Anomiidae and in Pectinidae the gonad opens into the external part of the renal tube.
This fact led Cuvier erroneously to the belief that a duct existed leading from the gonad to this papilla.
The essential reproductive organ or gonad consists of both ovarian and testicular cells (see fig. 42).
To this category will belong the oviducts in Teleostean fishes and probably the gonad ducts in several groups of invertebrates.
The gonad itself appears to represent a single median or bilateral organ.