1002.] CONKLIN — EMBRYOLOGY OF A BRACHIOPOD. 69 



against it. The fact that in both Phoronis and Lingula the intes- 

 tine forms a loop, the anus opening near the mouth, and that fixa- 

 tion takes place by the posterior extremity, has led to Caldwell's 

 view as to the homologies of the body surfaces in the brachiopods. 

 On the other hand the ventral mantle fold of Terebratulina forms 

 directly across the region where the blastopore lips fused and imme- 

 diately posterior to the place where the blastopore remnant closed and 

 where the mouth later appears. Upon the anterior face of this fold 

 the suboesophageal sense plate and ganglion appear; there can be 

 no doubt therefore that this fold is ventral in position. The dorsal 

 mantle fold appears at a very early stage (Figs. i6 and 20) on the 

 apical side of the gastrula and just posterior to the chief gastrula 

 axis ; it is impossible therefore that it should be considered as ven- 

 tral in position. Furthermore the mantle folds of the brachiopod 

 correspond to the zone which bears the tentacles in Actinotrocha (col- 

 lar, Masterman) and not to the margins of the ventral invagination ; 

 and since the mantle folds surround the body posterior to the 

 mouth, both of them cannot be ventral in position. Whether the pe- 

 duncle is ventral or not cannot perhaps be determined with certainty 

 until we know the embryology of a brachiopod in which the anus 

 and terminal portion of the intestine are present. In Lingula, as 

 is well known, the anus opens near the mouth and on the left side ; 

 in Crania it is terminal in position, and the embryology of either 

 of these forms should throw light on this question as to the mor- 

 phological position and homologies of the peduncle. Brooks' 

 work on Lingula deals only with stages in which the anus and the 

 intestinal loop are already present, and one cannot therefore tell at 

 what point relative to the blastopore the anus appears and how the 

 loop is formed. It is certain however that the ventral invagination 

 and remarkable metamorphosis of Actinotrocha are ccenogenetic 

 rather than phylogenetic characteristics, and that parallel phe- 

 nomena need not be expected in other groups of animals. Further- 

 more it is certain that the peduncle in Terebratulina is derived 

 from that portion of the gastrula which is posterior to the blasto- 

 pore ; I do not see therefore how it can be regarded as ventral in 

 position. But however this problem of the relation of the pedun- 

 cle of the brachiopod and the ventral invagination of Actinotrocha 

 may be decided by future work, it seems to me that the affinities of 

 Phoronis and Brachiopoda are well established. I agree therefore 

 in the main with the views of Caldwell, Lang and Blochman, and 



