406 E. W. MACBRIDE. 
affinities of Balanoglossus as put forward by Bateson, and then 
examine how Professor Spengel meets them. The Chordata 
are absolutely distinguished from all other Metazoa by three 
characteristics: (1) they have a dorsal central nervous system, 
separated from the skin by invagination and containing a 
central canal; (2) the anterior portion of the alimentary canal 
has paired gill-slits; (3) they have an endodermic rod, which 
has acquired a supporting function, and which is 
separated from the mid-dorsal gut-wall. All these struc- 
tures are found in Balanoglossus;! they have been 
sought elsewhere throughout the whole animal kingdom in 
vain. In addition to this, certain structures found in 
Amphioxus alone are compared to some of the peculiar 
structures of Balanoglossus. These are (1) the paired ante- 
rior enteric diverticula of Amphioxus, the left of which opens 
by a pore to the exterior, compared to the proboscis and its 
pore in Balanoglossus; (2) the covering of the gill-slits by a 
pair of atrial folds, from the walls of which a pair of excretory 
pores (the atrio-co:lomic funnels of Lankester) are developed, 
compared to the “atria” of B. Kowalevskii and the collar 
pores; (3) the secondary gill-bars, compared to the tongue- 
bars of Balanoglossus ; (4) the mouth adapted for digging in 
both instances. Whether any or all of this latter series 
of comparisons are valid is, however, of minor im- 
portance; the theory of the Chordate affinities of the 
Enteropneusta stands or falls with the validity of the 
comparison between nerve-cord, notochord, and gill- 
slits of Amphioxus, and the structures bearing the 
same name in Balanoglossus. 
With regard to the central nervous system, Professor 
Spengel maintains that it is only the part of the dorsal nerve- 
cord which belongs to the collar region; that it is found in the 
Tornaria as merely a part of this, the ventral nerve-cord being 
developed at the same time; and that the process of invagina- 
1 Throughout this discussion I use the name Balanoglossus as a general 
term, applicable to all the species of Enteropneusta, and do not in any way 
restrict its application to Spengel’s genus so named. 
