8 SIDNEY F. HARMER. 



the sections, as far as the ciliated ring. These two nerves 

 probably regulate the action of the cilia of the latter, and appear 

 further to give off fibrils to the thick ventral epiblast at the sides 

 of the pyriform organ. 



In fig. 3 may be seen the supposed nervous structures of 

 an old embryo in longitudinal section, the brain being connected 

 with the dorsal epiblast, as in fig. 4. 



In fig. 1, the region of the future brain is indicated by 

 hr. It is difficult to assert that any nervous .structures are at 

 present developed, but it may be noticed that the dorsal epiblast 

 is very much thickened above the pyriform organ. This character 

 is still obvious in embryos of the age of fig. 2, where it can usually 

 be seen (and often more distinctly than in fig. 2) that the dorsal 

 thickening of epiblast is so intimately connected with the ganglion- 

 cells of the brain that it can hardly be doubted that these cells 

 have been derived from the dorsal thickening itself. The origin 

 of the nerve-fibres is more difficult to ascertain. It is possible 

 that they may be developed from the dorsal side, and subsequently 

 enter into relation with the pyriform organ and other parts of 

 the ventral surface— or that they are developed partly from the 

 dorsal and partly from the ventral surface. Such sections as 

 figs. 3 and 4 seem to show that the nerve-fibres are not entirely 

 derived from the ventral surface, and it appears to me probable, 

 on the whole, that the greater part of the nervous system is 

 developed fi'oro. the dorsal epiblast. 



If it can be admitted that even a portion of the "brain" 

 has this origin, it then follows that we have in the larvse of 

 the Ectoprocta, as in those, of the Entoprocta, a development of 

 nervous tissue from the dorsal side of the ciliated ring, in the 

 anterior part of the embryo. The region just de scribed as "brain" 

 in Alcyonidium will thus be the homologue of the "dorsal organ" — ■ 

 .the supposed endodermic vesicle — of the Entopi'octa. It would be 

 interesting, in this connection, to know whether the pigment-spots 

 described by Nitsche (11) and others in the larva of Bugida are in 

 any way connected with this 'dorsal organ', as is the case with the 

 eyes of the larva of Loxosoma. 



The above conclusions do not allngcihcr agree with the 



