Materials and Methods
For the present paper a total number of 62 embryos and fetuses from ten cetacean species were investigated (Table 1). Several other species and specimens examined for the present study are not mentioned in Table 1 or in the subsequent chapters. These include, on the one hand, the very early embryonic stages, in which the nasal structures have not yet been quite clearly developed (Eschrichtius robustus, two specimens, Seattle collection), and on the other, species of a genus in which another closely related species has been examined, yielding similar results (Stenella coeruleoalba, 11 specimens, collection Seattle and collection Tokyo, and Stenella longirostris, six specimens, Frankfurt collection). One species is additionally included in a detailed comparison, although no material of it was available, but detailed data were found in the literature (Globicephala melas, according to the papers by Schreiber 1916 and De Beer 1937). The most valuable data were obtained on those species for which a continuous developmental series of several specimens was available. This was the case for Stenella attenuata, Delphinus delphis, Phocoena phocoena and Physeter catodon. Besides, there was an opportunity for another direct comparison with a total of 11 embryos and fetuses of four species, reported in the earlier literature (Kükenthal 1893; Boenninghaus 1903; De Burlet 1913a,b, 1914a,b, 1916; Honigmann 1917). However, these four species are represented in our own material as well, and therefore, the number of species examined has not been increased. Thus, the total is 92 specimens of 13 species of Cetacea, evaluated for the purpose of the present paper.
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