We have studied approximately 280 species spread over more than 100 families. New data on 80 species are reported. The spermatozoon of Chondrichthyes is characterized by two synapomorphies in the midpiece and the flagellum. Within the Chondrichthyes the subclass Holocephali is characterized by two spermatic apomorphies that distinguish it from the Elasmobranchii. The Osteichthyes, on the other hand, show great spermatic diversity. In each of the most primitive among them, the Actinistia, Dipnoi, Cladistia, Chondrostei, and Ginglymodi, the spermatic model is different, constituting many autapomorphies. The neopterygians possess a common character that distinguishes them from the other fishes: the lack of an acrosome. We propose a structure for the ancestral model of the spermatozoon of Neopterygii that resembles the gamete of aquatic invertebrates employing external fertilization. This simplified gamete exhibits several derived forms in teleosteans. It is mainly in the primitive Teleostei that these evolved forms are of taxonomic interest, as we demonstrate in the Mormyroidea and the Elopomorpha. In the evolved Teleostei we define a spermatozoon of the "perciform type." The distribution of this gametic type within the Perciformes may provide useful data for use with this ill-defined group whose phylogenetic interrelations are so little known.

Chondrichthyes possess an evolved type of spermatozoa. Their flagellar apparatus is characterized by the presence of flagellar roots which form the axis of the midpiece, and the existence of one or two lateral elements associated with the axoneme. Osteichthyes, mainly teleosteans, show a great diversity of spermatic forms. The primitive spermatozoon with a 9 + 2 pattern flagellum is common. The primitive spermatozoon has evolved along different lines. The spermatic diversity which results from this is mainly evident in the structure of the flagellar apparatus. In the animal kingdom the primitive spermatozoon with a 9 + 2 pattern flagellum, present in primitive metazoa, is retained in phyla where external fertilization is maintained. The main evolutionary tendencies--elongation, aflagellarity or biflagellarity--are generally connected with the acquisition of internal fertilization. These evolutionary tendencies are found in teleosteans. It is not possible to link aflagellarity or biflagellarity of the gamete in certain fishes to this method of fertilization. Only the elongation of the spermatozoon is connected, in certain cases, with internal fertilization, but this cannot be taken as general.

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