106 



ZYGODACTYLA CRASSA. 



Greenland (Fabricius) ; Maine, and Massachusetts Bay (L. Agassiz) ; 

 Nauslion (A. Agassiz). 



Cat. No. 277, Naushon, September, 1861, Alex. Agassiz. Medusa. 

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Zygodactyla erassa A. Agass. 



This species, which grows to almost as large a size as Zygodactyla 

 groenlandica, can be recognized at first glance by the small number 

 and great size of the genital organs ; there are not more than thirty- 

 two chymiferous tubes (Fig. 158) in a Medusa measuring ten inches in 

 diameter, while in a specimen of Z. groenlandica of the same size we 

 should find at least eighty to ninety ; the ovaries have an extraor- 

 dinary development, and bulge out at the time of spawning fully as 

 much as the ovaries of Melicertum, hanging very much in the same 



manner from the chymiferous tubes (Fig. 157) ; the radius of the 

 digestive cavity is larger ; the number of lips of the actinostome cor- 

 responds to that of the radiating tubes (Fig. 158) ; the digestive cavity 

 is far less capable of expansion and contraction than in Z. groenlan- 

 dica ; the marginal tentacles are much heavier and more massive ; the 

 color of the base is shghtly greenish-blue, as well as the genital 

 organs ; the latter have a rather more yellowish hue. Found at 



Fig. 1.57. Profile view of Zygodactyla erassa, somewliat reduced in size. 



