1884.] Balanoglossus Kowalevskii (Ayassiz), fyc. 



29 



while in Balanoglossus it is partial. In both, the backwardly- 

 projecting horn upon the left side becomes lined by ciliated columnar 

 cells and opens to the exterior. Moreover, in both animals .this 

 opening has a definite relation to the nervous system. In Amphioxus 

 it becomes the " olfactory " pit (Hatschek), while in Balanoglossus it is 

 surrounded by a mass of nervous tissue. Finally, the collar folds, 

 especially of B. Koivalevskii, would appear to be comparable with the 

 commencing atrial folds of Amphioxus, for the most anterior gill-slits 

 open into the cavity which is thus enclosed. 



The pair of ciliated funnels opening from the collar body cavities 

 to the atrium has been compared above to the excretory tube mentioned 

 by Hatschek in a similar position in Amphioxus. 



A pair of tubes has been described by Lankester in Amphioxus 

 opening into the back of the atrial cavity, communicating with the 

 dorsal body cavities. It may be remarked that if the collar fold of 

 J3. Kowalevskii were prolonged backwards, as the atrial folds are in 

 Amphioxus, the two collar funnels would then be carried backwards, 

 and have a relation similar to that of these tubes which, as suggested 

 by Lankester, may be excretory. 



To recapitulate : Striking resemblances to the Chordata and especi- 

 ally to the Cephalochord type are to be found in the following 

 structures : — 



(1.) The noto chord. 



(2.) The gills and branchial skeleton and blood supply. 

 (3.) The central nervous system. 

 (4.) The origin of the mesoblast. 



(5.) The peculiar fate and remarkable asymmetry of the anterior 

 pouch. 



(6.) The atria. 



(7.) The excretory funnels. 



In each of these cases, excepting that of the branchial structures 

 and the excretory funnels, the condition is that which would be 

 produced by a partial or arrested development of the corresponding 

 structure in Amphioxus. 



The a,bove considerations appear to justify us in including the 

 Enteropneusta among the Chordata. I would, therefore, tentatively 

 suggest the following table : — 



Chordata : — Hemichordata (Enteropneusta) . 

 Urochorda (Ascidians). 

 Cephalochorda (Amphioxus). 

 Yertebrata. 



It is not now proposed to enter into a more detailed discussion of the 

 morphology of the group, or of the light which an acceptance of this 

 suggestion throws on the origin of the Chordata. A fuller examina- 



