POLYZOA. 245 



becomes invested by a lining of cells, which Hatschek regards as 

 mesoblastic. A nearly similar organ to this is found in the embryo 



FlG. 130. TWO STAGES IN THE DEVELOPMENT OF PEDICELLINA. (After Hatscliek). 



v. vestibule; m. mouth; 7. liver; kg. hind-gut; a. anus; an.i. anal invagination ; 

 nph. duct of kidney; /</. ciliated disc; x. dorsal organ (probably bud). 



of Loxosoma [Vogt (No. 302) and Barrois (No. 298)]. Here however 

 it is double, and forms a kind of disc connected with two eye spots. 



Hatschek has made with reference to the dorsal organ the ex- 

 tremely plausible suggestion that it is a rudimentary bud, and that 

 the hypoblastic sack it contains gives rise to the hypoblast of the 

 young polype developed from the bud. Although, owing to the 

 deficiency of our observations on the attachment of the larva, this 

 suggestion has not received direct confirmation, yet the relations of 

 dorsal organs in Pedicellina and Loxosoma respectively strongly con- 

 firm Hatschek's view of their nature. Both of these forms increase 

 in the adult state by budding: in Pedicellina there is a single 

 row of buds formed successively on the dorsal side of the stem, 

 corresponding with the single dorsal organ of the embryo ; while 

 in Loxosoma a double row of buds, right and left, is formed, in 

 correspondence with the double nature of the dorsal organ. 



As to the mode of attachment of the embryo next to nothing is known, 

 the few observations we have being due to Barrois. From these observations 

 it would appear probable that the larva, as is usual amongst Polyzoa, 

 does not become directly converted into the permanent form, but that, 

 on becoming fixed, it undergoes a metamorphosis in the course of which its 

 organs atrophy. I would venture to suggest that the whole free-swimming 



