264 
T. Davidson — Wliat is a Brachiopod ? 
true representative of tbe gill plaits of the Lamellibranch, and bas 
notbing to do with tbe pharynx of tbe Bryozoon. Tbere are some 
characters of tbe Bracbiopoda tbat are very puzzling.” It is there- 
fore evident tbat tbe dismemberment of tbe Molluscoida must be 
considered necessary, and tbat we cannot place tbe Brachiopoda and 
Polyzoa in tbe same division witb tbe Tunicata. 
Tbe Bracbiopoda bave likewise been considered by Gratiolet, and 
some otbers, to be allied to tbe Crustacea. Morse reminds us also tbat 
twenty-six or twenty-seven years ago Prof. Steenstrup bad not only 
considered tbe Bracbiopoda as worms, but bad placed tbem near tbe 
tubicular annelids. 
It would not be possible, in this sbort paper, to enter into tbe 
numerous and elaborate details given by tliose zoologists in support 
of tbeir views, and the reader must consequently refer for more 
ample information to Prof. Morse’s several memoirs upon the sub- 
ject, and especially to tbe one on “ tbe systematic position of the 
Brachiopoda” publisbed in tbe Pr-oceedings of tbe Boston Society 
of Natural History, vol. xv., 1873, as well as to Kowalevsky’s im- 
portant mernoir publisbed in 1875. This last, bowever, written in 
tbe Russiau language, not being accessible to every reader, I cannot 
do better tban reproduce tbe sbort review publisbed by A. Agassiz 
in Silliman’s American Journal of Science and Art for 1874. “Tbe 
second memoir of Kowalevsky is a very complete liistory of tbe 
development of Brachiopods, strikingly in accordance with tbe views 
of Steenstrup, and of Morse, on tbe affinities of the Brachiopods 
Avitb Annelids. Tbe homology between the early embryonic stages 
of Argiope witb tbe known annelid larvaa is most remarkable, and 
tbe resemblance between some of tbe stages of Argiope figured by 
Kowalevsky, and tbe corresponding stages of growth of tbe so-called 
Loven type of development among annelids is complete. The number 
of segments is less; but otherwise tbe main structural features sbow 
a closeness of agreement wbich will make it difficult for concho- 
logists bereafter to claim Brachiopods as tbeir special property. 
Tbe identity in tbe ulterior mode of growth between the embryo of 
Argiope, and of Balanoglossus, in tbe Tornaria stage, is still more 
striking ; we can follow the cbanges undergone by Argiope wbile 
it passes through its Tornaria stage, if we may so call it, and becomes 
gradually, by a mere modification of tbe topograpby of its organs, 
transformed into a minute pedunculated Brachiopod, differing as far 
from tbe Tornaria stage of Argiope as tbe young Balanoglossus 
differs from tbe free swimming Tornaria. In fact tbe wbole develop- 
ment of Argiope is a remarkable combination of Loven’s and of 
Tornaria types of development among worms. His paper also in- 
cludes the history of a less vermiform type of development, tbat 
of Thecidium, and of Terebratula, in wbicb tbe observations of 
Kowalevsky fully r agree with the previous well-known memoir of 
Lacaze-Dutbiers on Thecidium, 1 and of Morse on Terebratulina ,* and 
it certainly is a striking proof of the sagacity of Morse to bave 
1 Annales des Sciences Naturelles, 4 6me Serie, Zool. vol. xv. 1861. 
2 Memoirs of the Boston Society of Natural History, vol. ii. 
