The spermatozoa differ from those of other animals in having the form of cells which sometimes perform amoeboid movements.
Though possessing a complete copulatory apparatus and producing large quantities of spermatozoa, they have lost their sexual instinct and play no part in the economy of the species.
Spermatozoa and ova.
The spermatozoa exhibit many differences in shape, size and proportions, in the various groups of birds.
They contrast with those of the Oligochaeta and Hirudinea by reason of their frequently close association with the gonads, the same organ sometimes serving the two functions of excretion and conveyance of the ova and spermatozoa out of the body.