296 ENTOPROCTA. 



is formed, lined with ciliated cells, which is capable of being 

 protruded as a papilla. The organ itself becomes invested by a 

 lining of cells, which Hatschek regards as mesoblastic. A nearly 

 similar organ to this is found in the embryo 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 

 extremely 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 confirm 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 observa- 

 tions 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 

 larva atrophies, while the dorsal organ alone develops into the fixed form 1 . 



Although the changes which take place during budding do not fall within 

 the province of this work, it may be well to state that Hatschek has 

 observed during this process the development of the nervous system and 

 the generative organs. The nervous system arises as an unpaired thickening 

 of the epiblastic floor of the vestibule, between the mouth and the anus. 

 On becoming constricted off from the epiblast the nerve ganglion contains a 

 central cavity which afterwards vanishes. 



The generative organs originate as a pair of specially large mesoblast 

 cells in the space between the stomach and the floor of the vestibule. These 

 two cells, surrounded by an investment of flattened mesoblast cells, sub- 



1 My view of the metamorphosis which takes place during the fixation of the 

 larva involves the supposition that in Loxosoma, about the attachment of which we 

 know absolutely nothing, two buds are directly formed in accordance with the double 

 nature of the dorsal organ. 



