Testicular material from a Blue Whale (Balœnoptera musculus Rafinesque), a Fin Whale (Balœnoptera physalus Lacepède) and a Sperm Whale (Physeter catodon L.), obtained 6–24 hours after death in the Antarctic during the whaling season 1946–47, showed that the testes of the first two animals were in the resting state and those of the third animal were active. Despite being collected some hours after death, the material has allowed estimation to be made for the first time of chromosome numbers from spermatogonia and spermatocytes in the prophase stage. The diploid and haploid numbers approximate to 48 and 24 respectively. These results are discussed along with those obtained by Makino (1948), the first worker to record counts of cetacean chromosomes, in his study of freshly fixed material from Dall's Porpoise, Phocœnoides dallii (True). They support this worker in his view that the cytological evidence indicates that Cetacea and Ungulata derive from a common source.

Some observations on spermateleosis and cell inclusions in the Sperm Whale are given.

Regarding the breeding season, the findings of previous workers are supported for the Blue and Fin Whales. That the Sperm Whale dealt with in this paper was found to be sexually active in December is support of Harrison-Matthews' view that the species has no definite sexual season or cycle.