of Mollusks in Holothuria?. 37 



Certain observations which I have made upon very young 

 Medusa? show, at all events, that there exist very young Medusa? 

 with all the attributes of a Medusa, which however move by em- 

 bryonic ciliary motion only, and evince none of the pulsating 

 contractions of adult Medusa?. 



It seems to follow thence that they may be the result of 

 sexual generation, and not of gemmation ; for the ciliated young 

 in Medusa?, as well as in Polypes, is the product of sexual gene- 

 ration. 



Since, however, this ciliated young has already the form and 

 organs of a Medusa, it appears to proceed directly from the 

 Medusa itself; for the Medusa? proceeding from the buds of 

 Polypes have no ciliary motion, and swim by the contraction of 

 their umbrella. 



To such forms as these belong the ciliated young of JEginopsis 

 mediterranea, Nob., described by me in the 'Archiv' for 1851; 

 and further, the young ciliated form described in the third Me- 

 moir upon the Echinodenn-larva?, pi. 7. figs. 9—11, and whose 

 nature, whether Echinoderm or Medusa, is there left undecided. 

 Lately, in Trieste, I have determined it to be a young Medusa 

 with otolithes ; the auditory vesicles are pedunculated, and con- 

 tain a round otolithe. A third young ciliated Medusa, with 

 6-10 unequal stiff marginal cirri, and 2-4 auditory organs with 

 otolithes, was observed by me in Trieste. The number of the 

 marginal cirri and pedunculated otolithe-sacs seems to increase 

 successively in this young form. The otolithes are simple and 

 round. The marginal cirri are divided by transverse partitions, 

 as in Polyxenia leucostyla of "Will, the young of which it probably 

 is. The body ©f the animal is ypth of a line in diameter. 



From all this we may conclude, that there exist young Me- 

 dusa?, with all the characters of Medusa?, in a very nearly em- 

 bryonic state, swimming merely by means of cilia, and not arising 

 by gemmation from Polypes, but very probably by direct sexual 

 generation from certain Medusa?. 



Observations on the preceding Article. 



The well-known care and accuracy of Prof. Miiller, and the 

 lucid manner in which he has detailed his observations, render 

 it impossible to entertain any doubts with regard to the facts 

 which he has discovered, and of which we have above endea- 

 voured to give an account as closely representing the original 

 as the peculiarities of a foreign tongue would permit. 



It is another affair, however, with regard to the deductions 

 from those facts, and (supposing the whole evidence in Prof. 

 Midler's possession to be before the public) we must eonfesa bo 



