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Memoir Sears Foundation for Marine Research 



tween length and weight in nasus is scant. Reported weights of about 400 pounds at nine to 

 ten feet, and 305 pounds at eight feet three inches would suggest that this is a much lighter 

 fish than oxyrinchus. But since the stoutness of its trunk suggests rather the reverse, it 

 seems more probable that the few reported weighings have been of fish that had been 

 gutted, which, in the case of a shark with so large a liver, means the loss of a large part of 

 the total weight. Females may contain embryos at a length of five feet. 



Figure 17. Lamna nasus, embryo, about 1 80 mm. long, from Barnstable, Massachusetts (Harv. Mus. Comp. 

 Zool., No. 35901), about 0.8 natural size. 



Develo-pmental Stages. It has long been known that this is an ovoviviparous species, 

 the young lying free in the uterus without connection with the mother. It also seems estab- 

 lished that in nasus, contrary to the rule among most other ovoviviparous sharks, the yolk 

 sac is absorbed and the umbilical cord entirely obliterated while the embryo is still very 

 small (55 to 60 mm.) and still with well developed external gills. Thereafter, the embryo 

 nourishes itself by swallowing the unfertilized eggs which lie close to it in the uterus, the 

 result being that its stomach becomes enormously swollen by the masses of yolk so swal- 

 lowed, forming a so-called "yolk stomach"}" as the embryo grows this increases in relative 



10. For more detailed accounts see Swenander (Zool. Stud. TuUberg, Uppsala, 1907 : 283, pi. 1) ; also, on the North 

 Pacific form, see Lohberger (Abh. bayer. Akad. Wiss., Suppl., f, Abt. 2, 1910). 



