30 MORPHOLOGY OF 



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 becoms the "olfactory" pit (Hatschek), while 

 in Balanoglossus it is surrounded by a mass of nervous tissue. 

 Finally, the collar folds, especially of B. Kowalevskii, 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 excre- 

 tory 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, com- 

 municating with the dorsal body cavities. It may be remarked 

 that if the collar fold of B. Kowalevskii were prolonged 

 backwards, as the atrial folds are in Amphioxus, the two collar 

 funnels would then be carried backwards, and have relation 

 similar to that of these tubes, which, as suggested by Lankester, 

 may be excretory. 



To recapitulate : striking resemblances to the Chordata, and 

 especially to the Cephalochord type, are to be found in the 

 following structures : 



(1) The notochord. 



(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 struc- 

 tures 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 above considerations appear to justify us in including 



