﻿264 T. Davidson — What is a Brachiopod ? 



true representative of the gill plaits of the Lamellibranch, and has 

 nothing to do with the pharynx of the Bryozoon. There are some 

 characters of the Brachiopoda that are very puzzling." It is there- 

 fore evident that the dismemberment of the MoUuscoida must be 

 considered necessary, and that we cannot place the Brachiopoda and 

 Polijzoa in the same division with the Tunicata. 



The Brachiopoda have likev/ise been considered by Gratiolet, and 

 some others, to be allied to the Crustacea. Morse reminds us also that 

 twenty-six or twenty-seven years ago Prof. Steenstrup had not only 

 considered the Brachiopoda as worms, but had placed them near the 

 tubicular annelids. 



It would not be possible, in this short paper, to enter into the 

 numerous and elaborate details giA^en by those zoologists in support 

 of their views, and the reader must consequently refer for more 

 ample information to Prof. Morse's several memoirs upon the sub- 

 ject, and especially to the one on " the systematic position of the 

 Brachiopoda" published in the Proceedings of the Boston Society 

 of Natural History, vol. xv., 1873, as well as to Kowalevsky's im- 

 portant memoir published in 1875. This last, however, written in 

 the Eussian language, not being accessible to every reader, I cannot 

 do better than reproduce the short review published by A. Agassiz 

 in Silliman's American Journal of Science and Art for 1874. "The 

 second memoir of Kowalevsky is a very complete history of the 

 development of Brachioi^ods, strikingly in accordance with the views 

 of Steenstrup, and of Morse, on the affinities of the Brachiopods 

 with Annelids. The homology between the eaidy embryonic stages 

 of Argiope with the known annelid larvae is most remarkable, and 

 the resemblance between some of the stages of Argiope figured by 

 Kowalevsky, and the corresponding stages of growth of the so-called 

 Loven type of development among annelids is complete. The number 

 of segments is less: but otherwise the main structural features show 

 a closeness of agreement which will make it difficult for concho- 

 logists hei'eafter to claim Brachiopods as their special property. 

 The identity in the ulterior mode of growth between the embryo of 

 Argiope, and of Balanoglossus, in the Tornaria stage, is still more 

 striking ; we can follow the changes undergone by Argiope while 

 it passes through its Tornaria stage, if we may so call it, and becomes 

 gradually, by a mere modification of the topography of its organs, 

 transformed into a minute pedunculated Brachiopod, difiering as far 

 from the Tornaria stage of Argiope as the young Balanoglossus 

 differs from the free swimming Tornaria. In fact the whole 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, that 

 of Thecidium, and of Terehratida, in which the observations of 

 Kowalevsky fully agree with the previous well-known memoir of 

 Lacaze-Duthiers on Thecidium,'^ and of Morse on Terebratulina,'^ and 

 it certainly is a striking proof of the sagacity of Morse to have 



' Annales des Sciences Naturelles, d'^^e serie, Zool. vol. xv. 1861. 

 ^ Memoirs of the Boston Society of Natural History, vol. ii. 



