I 20 



surroiindiiii^ the mouth and following the bases of the lophophore and lower lip ; or, in other 

 words, having the form of two crescents facing in the same direction and united at their tips. 

 This double crescent extends into the lower lip, and sends off branches into the tentacles; and 

 Shipley suggests that it may be homologous with the "anterior body-cavity" of Phoronis\ that 

 is, with the praeseptal space which perhaps represents the collar-cavit\-. If there is anything in 

 this suesrestion, and if the arrangement has an\' rt:Iation to what is fountl in the Hemichordata, 

 it is necessary to suppose that the proboscis has been greatly reduced — if it l)c not altogether 

 absent — in PJiyscosonia as in PJioronis. 



On the other hand Gerol'Ld ') considers that the transitory metamerism which he has 

 observed in the larva ci{ Phascolosoma^ together with other features, "indicate the close relationship 

 between the Sipunculids and the Annelids". It appears however, from an earlier part of the 

 .same preliminary note that the metamerism consists of a division into four segments, noticed 

 in the nerve-cord and in the mesoblastic bands immediately before the metamorphosis. This 

 question of metamerism in Sipunculids is clearly one of great importance, but the small number 

 of metameres mentioned by Gerould suggests the possibility that the arrangement is not 

 fundamentally difterent from that found in the Hemichordata. 



Here, as in the case of the Brachiopoda, which are next considered, it appears to me 

 that affinities to the Hemichordata may ])erha]js exist, but that the pre.sent state of our knowledge 

 does not juslif\- any positive statement on the subject. 



The affinity of the Brachiopoda to the Hemichordata has been maintained by Masterm.\x 

 (98, i); while it was suggested some years earlier by Caldwell (83) that these animals are 

 related to Phoronis. In this connexion reference may be made to a recent embryological paper 

 by CoNKLix ■), who comes to the conclusion (p. 69) that "the affinities of Phoronis and Brachio- 

 poda are well established", and (p. 70) that except for the absence of segmentation in the 

 coelom, "there are no important differences between Actinotrocha and the brachiopod larva". 



The account given by Conklix is a confirmation of the general accuracy of the figures 

 published by Kowalevskv in 1874. The development of the Brachiopoila, as indicated by these 

 two observers, shews certain resemblances to that of the Enteropneusta and of Ccphalodiscus. 

 There is, for instance, a conspicuous anterior region of the body-cavity which is developed as 

 an unpaired enterocoel from the front of the archenteron. The manlle-fold of the young larva 

 forms a more or less equatorial swelling, which gives rise to the a])pearance of a division of 

 the entire larva into three segments. Masterman (98, i, p. 288) gives a figure indicating that the 

 second of these "segments" (the mantle-fold) is the equivalent of the collar of the Enteropneusta, 

 al. hough he explains on the preceding page that the arms as well as the mantle are to be 

 regarded as derivatives of this region. From the account which has recently been given by 

 Yatsu ') of the development of IJiigu/a, it would, however, appear that the arms develop from 

 a region which is in front of that of the mantle-fold ; and it is not easy to assume that both 



i) J. H. Gerould, "The Development of Phascolosoma"^ Arch. Zool. Exp. et G6n. (4) 11, Notes ct Revue, 1904, NO 2, p. xvii. 



2) E. G. CONKLIN, "The Embryology of a Brachiopod, Tcrcbratuliiia septeitlrioiiaUs'^\ Proc. Amer. Phil. Soc. XLI, 1902, p. 41. 



3) N. Vatsi', "On the Development of Lingula anatina'\ Journ. Coll. Sci. Tokyo, XVII, 1901 — 1903, Art. 4. 



