4.04. E. W. MACBRIDE. 
the metamorphosis of the larva into the young worm, he has 
not seen the development of the notochord or central nervous 
system. His youngest larve had a complete gut with mouth 
and anus, and the proboscis celom opening already by its pore. 
He has shown that the muscle connecting the apical plate or 
brain with the proboscis cavity is really double, and that its 
sheath is continuous with the peritoneum of the proboscis 
cavity. Morgan,! in his last paper, which has appeared since 
the publication of the monograph, confirms this, and goes 
further ; he finds that the anterior unpaired part of the muscle 
is an anterior prolongation of the proboscis cavity, and that 
the paired portions are formed from its lateral walls, and 
hence these muscles are strictly comparable to the 
muscles of the preoral lobe of Asterid larve. Thus 
one of the few resemblances to the trochosphere which 
Tornaria was supposed to exhibit is cancelled. The only im- 
portant organ, the origin of which Spengel has satisfactorily 
determined, is the trunk ceelom, and here his results confirm 
those of Bateson. In reading his discussion of the morphology 
of Tornaria he gives one the impression that he has seen the 
origin of the collar celom. This is not so, as can be seen 
by a reference to the chapter on Ontogeny. He assumes 
that it is segmented off from the front end of the trunk ccelom, 
a supposition which is in contradiction to the results of both 
Bateson and Morgan. 
He believes that he has seen the collar pore arising as an 
outgrowth of the first gill-sac. This view of its origin, which 
is maintained in opposition to that of Bateson, who regarded 
it as arising as a thickening of the skin on the posterior free 
edge of the collar, is founded on the examination of one 
specimen mounted whole. In his last paper Morgan 
figures sections showing that Bateson’s view is perfectly right. 
He tells us that there is an ectodermic invagination giving rise 
to the collar pore at its upper end, and that both the first 
and the second gill-sacs open into it in the species he 
1 T. H. Morgan, ‘‘ The Development of Balanoglossus,” ‘Journal of Mor- 
phology,’ vol. ix. 
