Ixviii. PRESIDENT'S ADDRESS. 



the Molluscoidea, like that of the Zoophytes, is effected by 

 gemmation, as well as by the true generative process. The 

 gemmae are sometimes detached so as to be able to make their 

 way freely through the water; frequently they remain con- 

 nected with the parent-structure, and with each other, so as to 

 to form aggregate families and in this respect resemble Zoophytes. 

 In the lowest group, the generative apparatus is united in the 

 same individual, but in the highest the sexes are completely 

 distinct. Again a considerable number of individuals of the 

 lower group are fixed to one spot excepting during the early 

 periods of their existence, their food is conveyed to them by 

 ciliary currents, and they pass an inactive life like that of plants. 

 The Tunicata hold a place intermediate between the Bryozoa 

 and the Brachiopoda. The lower sections of the Order are 

 allied to Bryozoa in their tendency to increase by gemmation, 

 they are more inactive in their habits, exhibiting scarcely 

 anything like the rapid movements of retraction and expansion 

 which are so interesting to watch in the Bryozoa. The higher 

 forms lead a solitary life, the gemmae becoming detached before 

 their development is far advanced. It is among them we find an 

 approximation in general structure to the type of the Bivalve. 



The body of the Ascidians, one of the principal divisions of 

 Tunicata, is usually completely enclosed within a general integu- 

 ment, or tunic, having two orifices, a mouth and a vent ; it is 

 tough, leathery, or even cartilaginous, and made all the more 

 resisting by the agglutination of sand, small gravel, &c., which 

 almost takes the place of a shell. The young in the early stage 

 of life have the power of locomotion, and after swimming about 

 for a time, attach themselves to some object, and after passing 

 through various phases, assume the adult form. 



The Brachiopoda, the highest of the group, receive the name 

 from the long arms, fringed with filaments, springing from either 

 side of the mouth, and occupying a considerable portion of the 

 cavity of the shell ; they do not appear to have any organs of 

 prehension in the living Brachiopoda ; they are incapable of 

 extension. It is possible their special purpose is to create 



