The SPERMATOZOA of the Apoda and Urodela have an undulating membrane along the tail, while the head-end is either pointed or truncated. Those of _Spelerpes fuscus_ and of _Ichthyophis glutinosa_ measure about 0.7 mm. in total length, those of the other Urodela being much smaller. A peculiarity of the Urodela is that their spermatozoa are massed together in or upon spermatophores, an arrangement which undoubtedly facilitates the internal {53}fecundation of the female without actual copulation. The female takes up such a deposited spermatophore with the cloacal lips, squeezes the sperma out of the capsule which remains behind, and either conveys the former into a special receptaculum seminis, _e.g._ in _Salamandra atra_ and in _Triton_, or the spermatozoa wriggle their way, thanks to the undulating tail, directly up the oviducts to the ova. The spermatophores are composed of a colourless, soft, gelatinous mass, which is probably produced by the cloacal gland. The shell of jelly is in fact a cast of the cloacal cavity, reproducing all its ridges, furrows and folds, while a toad-stool-shaped papilla of the cloaca makes the inside lumen of the cast, _e.g._ in _Triton_. Those of _Salamandra maculosa_ are much simpler, consisting, in conformity with the absence of a cloacal papilla, merely of a cone with a globular mass of sperma on the top. Those of _Amblystoma_ are similar. The spermatozoa of the Anura show considerable differences in the various genera, of which, however, only the European forms have been properly examined. The "head" is wound like a corkscrew in _Discoglossus_, _Pelobates_, and _Pelodytes_; spindle-shaped, more or less curved, in _Rana temporaria_ and _R. agilis_, _Hyla_, _Bufo_ and _Bombinator_, in the latter with an irregular membrane on one side; cylindrical in _Rana esculenta_ and _R. arvalis_. The tail is mostly long and filiform, but in _Bufo vulgaris_ and _Discoglossus_ it is provided with an undulating membrane. Their size is generally very small, only about 0.1 mm., excepting those of _Discoglossus_ which reach the astonishing length of 3 mm. These differences in shape, especially that of the head, explain why species of the same genus, e.g. _Rana temporaria_ and _R. arvalis_, cannot fertilise each other. [Illustration: FIG. 8.–A bell-shaped spermatophore of _Triton alpestris_. × 3. (After Zeller.)[25]]