I 20 



surrounding- the mouth and following the bases of the lophophore and lower hp ; or, in other 

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

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

 Shipley suo-CTests that it may be homologous with the "anterior body-cavity" oi PIioronis\ that 

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

 this suo-o-estion, and if the arrangement has any relation to what is found in the Hemichordata, 

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

 absent — in Physcosoina as in Phoi'onis. 



On the other hand Gerould ^) considers that the transitory metamerism which he has 

 observed in the larva o{ 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 different 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 perhaps exist, but that the present state of our knowledge 

 does not justify any positive statement on the subject. 



The affinity of the Brachiopoda to the Hemichordata has been maintained by Masterman 

 (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 CoxKLiN '), 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 difterences between Actinotrocha and the brachiopod larva". 



The account given by Coxklin is a confirmation of the general accuracy of the fio-ures 

 published by Kowalevsky in 1874. The development of the Brachiopoda, as indicated by these 

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

 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 mantle-fold of the young larva 

 forms a more or less equatorial swelling, which gives rise to the appearance 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 Lingula, 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 Pliasco/osoma'\ Arch. Zool. Exp. et Gén. (4) II, Notes et Revue, 1904, N» 2, p. xvii. 



2) E. G. CONKLIN, "The Embryology of a Brachiopod, Tcrebratulina septentrioiialis"\ Proc. Amev. Phil. Soc. XLI, 1902, p. 41. 



3) N. Yatsu, "On the Development of Liiigiila aiHitiiia\ Journ. CoU. Sci. Tokyo, XVII, 1901 1903, Art. 4. 



