On the Dm'atiou of Gravidity in Certain Odontoceti. 



T 



he question as to how long the Cetacea are pregnant has interested naturalists as long as any cetological literature has 

 been in existence, even Aristotle (1) having discussed this side of the biology of the Dolphin. In the opening short literary 

 survey, it will be seen that this interesting question has been touched upon by the most various authors. 



It is, however, only recently that the subject has been more scientifically handled. In addition to Eschricht 

 (40 and 41), van Beneden (84), and others, G. Guldberg (57), nearly ten years ago made a more careful investigation 

 of the matter with regard to the family Balænopteridæ. In more recent times, James A. Grieg') in Bergen has taken 

 up the same theme for treatment, and made some important contributions to it, especially with regard to Balænoptera 

 rostrata and Phocæna communis. Although I am not at present able to shed much new light upon this question, any 

 contribution, however small, is sure to possess a certain amount of interest. 



1. Coiicerniiiu; Gravidity in Lasenorliynchus acutus, Gray. 



According to the hitherto known measurements of this species, the length of the full-grown male must be taken as 

 2. .5 metres and over, while the female does not attain to that length, being 2.4 metres, or rather less. 



Of the fretuses now under discussion. I believe the one measuring 0.95 metres in length to be a ftdly-developed 

 specimen. According to this, the fully-developed young one measm-es -/s of its mother's length. The female foetuses are 

 probably somewhat smaller than the male, just as the fully-developed females are smaller than the males. 



For determining the time of gravidity and its duration, we have the following data from the specimens before us. 



In the beginning of November, the fætuses vary from 26 millim. to 170 millim., the smallest 8 millim. long 

 embryo not being taken into consideration, as it cannot be looked upon as normal. Most of them, however, have a length 

 of 140 millim. 



In December, a foetus of 195 millim. in length was observed. 



In February, a foetus was observed with a length of 455 millim., thus being half developed as regards its length. 



In May and June, 4 foetuses were observed, 3 of which were more nearly developed — • 760 to 820 millim. — 

 and one almost fully developed ("full grown'') 950 millim. On June 2nd, 1885, according to information kindly given by 

 Prof. R. Collett, a foetus 850 millim. in length was acquired by the Stavanger Museum. 



According to this, the young should be born in the spring before or about Midsummer, and this also 

 agrees with observations made in other quarters. Thus in the month of June, 1842, in the haul taken at Drøbak, milk was 

 found in the breasts of 4 females. Prof Rasch, however, does not mention having seen small young ones. 



Prof. Collett (Nyt Mag. f. Naturvidensk. Bd. 2, 1877, pag. 143) mentions a specimen taken on the 8th June, 

 1867, of which the mammary glands were full of greyish yellow milk, an observation which agrees with my own supposition. 



No observations, however, have been made concerning the time before copulation which may probably be placed 

 in the month of .August; the period of gravidity would then be about 10 months. 



') CetDloi^iske notispv. pa^. 8 — 16, in Bergens Museurasi Aarsberetning. 1889. 



