OF MKDUS.E MAUK HY WILLIAM KKITH HKouKS. i 



it is commonly infested by larvae of Cunoctantha octonarta McCrady, although it appears to 

 be quite immune from this parasite in other places. I can detect no specific distinctions 

 between this medusa and " Turritopsis pol\'cirr/ni," which is occasionally seen off the Atlantic 

 coast of France and Germany. This form is well figured by Keferstein, 1862, and Hartlaub, 

 1897, who are the only European students who have observed the medusa on the eastern side 

 of the Atlantic. 



W.HS: 



Fic. 76. Turritofisis nulnciila, after Brooks, in Mem. Boston Soc. Nat. Hist. Hydroid and young medusa. 



Rittenhouse, 1907, has made an elaborate study of the development of T. nutncula. 1 he 

 ova develop in the ectoderm of the 4 interradial sides of the manubrium. The primitive ova 

 grow by the absorption of ovarian cells around them, as is common in other hydromedusae. 

 The yolk-spheres in the ovum are formed from the ovarian cells which it absorbs. About 20 to 

 35, rarely 50 or more, eggs are discharged into the water by the muscular rupture of the ovar- 

 ian walls between 5 and 6 o'clock in the morning. The discharged eggs are spherical, 0.116 

 mm. in diameter and have no membrane. They are yellowish-white, heavier than sea-water, 

 and opaque. The outer layer of finely-granular ectoplasm is distinct from the coarsely gran- 

 ular, yolk-laden endoplasm. Soon after being discharged the egg gives off two polar bodies 

 and is fertilized. Segmentation is total and approximately equal. The first two segmentation 

 planes are meridional and the third equatorial. The blastomeres remain quite tar apart, 



