328 



MEDUSA OF THE WORLD. 



The gonads may be bilamellar or linear, or linear with swollen, knot-like intervals. 

 The color ranges through blue, gray, brown, rose-red, violet, milky-white, or colorless. 

 Haeckel's specimens were from the Mediterranean and Atlantic coasts of Europe. Making 

 all due allowance for the description of growth-stages and of regenerating or injured speci- 

 mens, it is evident that we here have a medusa which appears to be as variable as Aurelia 

 among the Scyphomedusae. 



The bell is usually somewhat flatter than a hemisphere, with thick, gelatinous center, 

 thinning out to a sharp-edged margin. The center of the bell is often biconvex. The largest 

 of 28 specimens obtained by Claus, 1883, in the Mediterranean, were about 150 mm. wide, had 

 67 radial-canals, 66 lips, 1 1 1 tentacles, 300 to 400 lithocysts, and his specimens ranged in color 

 from blue or light-rose to colorless. 



When the medusa is 1.5 mm. wide there are 4 well-developed radial and 4 small interradial 

 tentacles, 8 adradial lithocysts, and no gonads. The gonads begin to develop upon the radial- 

 canals of the three oldest orders when the medusa is about 35 to 60 mm. wide. They are, 

 however, very irregular in development and may appear equally developed and all small 

 when there are 70 radial-canals and the medusa is 100 mm. wide; or the gonads may be 

 developed on only 32 (half) of the 65 radial-canals when the medusa is 75 mm. wide. Usually 

 a few canals fail to develop gonads. A thickening of the gonads along the edges of the radial- 

 canals gives a bilamellar aspect to the gonads, whereas in a less vigorously developed state 

 they appear to be merely linear, or linear with knot-like swellings at intervals. 



There are conical, excretory papillae at the bases of the tentacles on the subumbrella side, 

 above the velum. 



Browne, 1903, calls attention to certain varieties in shape of the tentacle-bulbs of speci- 

 mens of jEquorea, but I can not feel convinced that some, or possibly all, of these differences 

 may not be due to states of development or of contraction. 



In 1897 Browne gives the following data from a study of 5 specimens of ALrjiiorea for- 

 skalea from Valencia Harbor off the southern coast of Ireland: 



The development has been studied by Wright (Journal Microscop. Science, London, 

 New Series, vol. 3, p. 45, plate 4, figs. 1-6), who reared the hydroid from the egg of the 

 medusa. 



The early stages of development of the egg have been studied by Claus, Metschmkoff, 

 and Haecker. The sexual products are cast out near sunrise, in March and April, in the 

 Mediterranean. The males are more bluish and the females more rose-colored in their 

 sexual organs. The egg is 0.16 mm. wide. Segmentation is total but not equal, the oval 

 blastula having small cells at the animal and large spindle-shaped cells at the vegetative pole. 

 The entoderm is formed by ingression of cells from the narrow, posterior end of the larva. 



