kidney, and serves merely as a vas deferens or sperm duct. In correlation with this it is somewhat enlarged, especially in its posterior portion, to form a vesicula seminalis. The morphological interest of these features lies in the fact that they represent a stage in evolution which carried a little farther would lead to a complete separation of the definitive kidney (_metanephros_) from the purely genital anterior section of the mesonephros (_epididymis_), as occurs so characteristically in the Amniota. Dipneusti.--In _Lepidosiren_[24] a small number (about half a dozen) of vasa efferentia occur towards the hind end of the vesicular part of the testis and open into Malpighian bodies. In _Protopterus_ the vasa efferentia are reduced to a single one on each side at the extreme hind end of the testis. [Illustration: Graham Kerr, _Proc. Zool. Soc. London_. FIG. 12.--Diagram illustrating Connexion between Kidney and Testis in Various Groups of Fishes. A, Distributed condition of _vasa efferentia_ (_Acipenser_, _Lepidosteus_). B, _Vasa efferentia_ reduced to a few at the hind end (_Lepidosiren_). C, Reduction of vasa efferentia to a single one posteriorly (_Protopterus_). D, Direct communication between testis and kidney duct (_Polypterus_, Teleosts). c.f, Nephrostome leading from Malpighian coelom into kidney tubule. T1, Functional region of testis. T2, Vesicular region of testis. WD, Mesonephric duct.] Teleostomi.--In the actinopterygian Ganoids a well-developed testicular network is present; e.g. in _Lepidosteus_[25] numerous vasa efferentia arise from the testis along nearly its whole length and pass to a longitudinal canal lying on the surface of the kidney, from which in turn transverse canals lead to the Malpighian bodies. (In the case of _Amia_ they open into the tubules or even directly into the mesonephric duct.) In the Teleosts and in _Polypterus_ there is no obvious connexion between testis and kidney, the wall of the testis being continuous with that of its duct, much as is the case with the ovary and its duct in the female. In all probability this peculiar condition is to be explained[26] by the reduction of the testicular network to a single vas efferens (much as in _Protopterus_ or as in _Raia_ and various anurous Amphibians at the front end of the series) which has come to open directly into the mesonephric duct (cf. fig. 12).