BRACHIOPODA. 7 



rate essay on the Thecidium Mediterraneum will be 

 found in the ' Annales des Sciences Naturelles ' for 1861, 

 and is the first of a series of monographs on the organi- 

 zation of the living Brachiopoda. He asserts most con- 

 fidently that the Thecidia are of different sexes, and 

 that the male and female can be distinguished even by 

 their shells. According to his observations the embryo 

 of Thecidium is divided into four distinct lobes, and it 

 has sometimes two, and at other times four eye-spots. 

 When separated from the peduncle by which it is 

 attached, it swims or whirls head foremost by means of 

 vibratory cilia which cover the body. Fritz Miiller had 

 previously described in Wiegmann's Archiv (xxvii. p. 53) 

 the fry of a Brazilian Brachiopod. He says it was enclosed 

 in a bivalve shell like the adult, and that its structure 

 was the same, except in having two eyes and in wanting 

 the reproductive and circulatory organs. The arms were 

 covered with a complete coat of cilia, by the action of 

 which the little creature swam. It could also creep ; 

 and this was effected by a semirotatory movement 

 alternately to the right and left, and by pushing itself 

 along by means of the bristles or setae which fringe the 

 edges of the mantle, and upon the strongest of which it 

 would occasionally support itself while resting. The 

 Brachiopoda are extremely prolific, and their countless 

 eggs are of a spherical shape. After quitting the em- 

 bryonic state, they become invariably and permanently 

 fixed to other substances, being incapable of any other 

 motion than making a half-turn round the peduncle or 

 pivot. Their food consists of Infusoria or other minute 

 organisms. Milton has, with his usual felicity, de- 

 scribed the present animals as those which, 



" in their pearly shells at ease, attend 



Moist nutriment." 



