NOTES AND MEMORANDA. 341 



Halosphaera viridis, Sclimidt, — This marine alga was found liere 

 last spring. It lias been observed at Naples, but its life-history is very 

 imperfectly known. It consists of a hollow sphere from a quarter to 

 half a millimetre in diameter, the inner surface of which is covered by 

 a thin layer of protoplasm containing numerous chlorophyll granules 

 embedded in it, and a large nucleus which is surrounded by a mass 

 of protoplasm free from chlorophyll. These spheres float in great 

 numbers close to the surface of the sea, and are carried about by the 

 waves, having- no motion of their own. F. Schmitz, the only observer 

 who has recorded any observations on them, states (Mittheil. aus d. 

 Zool. Stat, zu Neapel, Bd. i, 1879) that these spheres always make 

 their appearance at Naples in January or February and remain till 

 June, when they disappear. During that time he observed repeated 

 division of the nucleus to take place, accompanied by spindle forma- 

 tion, as the result of which the contents of the sphere are converted 

 into a large number of daughter-cells consisting each of a nucleus 

 surrounded by a mass of protoplasm, to which the chlorophyll, now 

 diffused, gives a dense green colour. These daughter- cells adhere 

 to the wall of the sphere, which consists of two envelopes, an outer 

 and an inner. The outer one bursts, and the inner one gradually 

 dissolves away, setting free a number of zoospores to which the 

 daughter-cells above mentioned have meanwhile given rise by sub- 

 division. These zoospores are conical cells furnished with a pair of 

 cilia springing from the basal end of the cell. They swim about 

 freely. Beyond this their history has not been traced. Our know- 

 ledge of its development is thus insufficient to enable us to determine 

 the systematic position of Halosphgera, Specimens found at Plymouth 

 were sent up to London for examination in April last, but owing to 

 defective conditions it was not possible to keep them alive long enough 

 for observation. I hope an opportunity may be found of studying 

 them under more favorable circumstances next spring. — HERBERT 

 THOMPSON. 



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