90 



<2, the tentacles of the second set, half-way 

 between those of the first set. Fig. 2 is a 

 more advanced stage of StauropJiora, in which 

 the tentacles of the third set are almost as 

 large as those of the first and second sets, and 

 the fourth, fifth, and sixth sets of tentacles 

 can readily be distinguished. Using the 

 same notation as above, the formula for the 

 tentacles would be : 



J-l) fg' 4' 3' ^5' ^7' ^2» ^7' ^5' ^3' ^4' ^6' "'"l" 



In fig. 3, the young Siaurophora has a still 

 Fig. 3. 



Fig. 2. 



Young Siaurophora, slight- 

 ly older tliuu tig. 1. 



Young StauropJiora, still older 

 tliau tts>'. 2. 



greater number of sets of tentacles, the 

 fourth and fifth sets having grown suffi- 

 ciently large to be easily distinguished 

 from one another by their difference in 

 size ; the eighth and ninth sets have 

 made their appearance. The formula 

 for this stage of growth is ; T^^ , t^, t^, t^, 



''31 ^9' ^5' ^7' ^2' ^7' ^5' ^9' ^35 ^8' ^4' ^6' 1' 



The number of tentacles of the first set 

 are four (4 T^) ; there are in the second 

 set also four ('4i? 2), using the same nota- 

 tion; there are in the third set 8^3; in 

 the fourth set 8 i^ ; in the fifth set 8 t^ ; 

 in the next set 8t^; then 8tg, and St^ in the ninth set. The 

 number of tentacles which Siaurophora may have at any particular 

 time can easily be found, and the formulas for the number of tenta- 

 cles in figs. 1, 2, 3, would be : 



2 t ^ 4 Tj -f 4 ^2 5 or 8 tentacles for fig. 1, 

 2 1 denoting the sum of the different sets of tentacles round the 

 circumference ; 



2 t = 4 Ti + 4 ^2 + 8 <3 + 8 «4 + 8 <g + 8 <s + 8 f^ for fig. 2, 



or forty-eight tentacles ; and, finally, 



2 t = 4 Ti + 4 ^2 + 8 <3 + 8 «4 -f 8 ^5 + 8 <e + 8 <7 -f 8 ^8 + 8 <9, 



or sixty-four tentacles in fig. 3 ; and so on as far as the seven- 

 teenth set. It becomes almost impossible to follow the development 

 of the tentacles further, as they are then rather irregular in their 

 growth, and often much more numerous in one quarter segment than 

 in the adjoining one. In fig. 3, we have the first sign of the de- 

 velopment of the ovaries, the corners of the digestive cavity ex- 

 tend, little by little, along the chymiferous tubes, and when the 

 young Medusa has attained the size of an inch in diameter, the 

 ovaries already reach half-way towards the circular tube. For 



