Morse.] * § 6 0 [March 19, 
openings, which are very small and difficult to notice; the one to 
take in, the other to eject the water,” etc. 
The branchial sac was also believed to be the homologue of the 
gills of the Lamellibranchiate Mollusk, though Hancock! has shown 
that the branchial sac of the Ascidian is not the anatomical equiva- 
lent of the gills of the Lamellibranch, but is a portion of the alimen- 
tary canal. / 
| Milne Edwards, in his splendid memoir on the composite Ascid- 
ians,? in speaking of their molluscan affinities, said that these 
relations were far less intimate than was usually believed, and that 
they departed from the Mollusca in their mode of circulation, in the 
metamorphosis which their fry passed through, and more particularly 
in the singular feature that most of them possessed in multiplying by 
gemmation. 
Now since the Polyzoa are placed with the Vermes by Gegenbaur 
and others, and indeed were long ago placed there by Leuckart, 
while the Tunicates have been assigned to the Vermes by many of 
the most eminent German investigators, while others still would place 
them at the foot of the Vertebrate series, it is unnecessary for me 
to consider the affinities of the Brachiopods through their relations 
with these groups. 
-Kowalevsky, Kupffer, Schultze and others, assign the Tunicates a position 
at the base of the Vertebrate series, through the unquestionable affinities of 
certain of their forms to Amphioxus, as well as their singular embryological re- 
lations with the Vertebrates. In this connection it is instructive to note that 
Gegenbaur sees a relation between the branchial sac of Balanoglossus, and 
the branchial sac of an Ascidian. 
In the year 1848, the far seeing Leuckart was inclined to believe that the 
Tunicates formed an intermediate class between the Echinodermata and the 
Vermes, while others traced a resemblance between certain Nemertean larva 
and the early stages of the Echinoderms, causing Huxley to unite the Echino- 
dermata with the Articulates. And lastly, a Tornaria described by Miller, 
Krohn and Alex. Agassiz, was taken to be an unquestionable Echinoderm larva, 
Now thanks to the brilliant investigations of Mr. Agassiz,4 this Tornaria turns 
out to be the young of that odd worm Balanoglossus; though Mr. Agassiz finds 
a wide gap between the Tornaria of Balanoglossus and the Echinoderm young, 
vet he admits the striking resemblance between the two. He says, “ This 
remarkable type recalls the Tunicates, from the nature of its gills and mode of 
1 Annals Nat. Hist. 4th Series, Vol. v., p. 196. 
2 Memoires del’ Acad. des Sciences. T. xvitt, 1842. 
3 Early Stages of an Ascidian. Proc. Bos. Soc. Nat. Hist., Vol. xIv., p. 351. 
$ The History of Balznoglossus and Tornaria. Mem. Amer. Acad., Vol.1x., p. 404. 
