1 2' 



The lateral praeoral cavities are derived from the collar-cavities, and are in fact the 

 antero-dorsal processes shewn in Hatschek's well known figs. 50 — 52 (81) of an embryo of 

 AmphioxLis. The remainder of the collar-cavities is constituted by the right and left stomocoels, 

 together with at least three myotomes (p. 68), and the anterior parts of the metapleural canals. 

 These had been supposed by MacBride, in his earlier paper (98), to belong entirely to the 

 collar, but van Wijiie considers that their innervation shews that they belong for the most 

 part to the metasome, only their anterior ends belonging to the collar. The collar thus ends, 

 as in Enteropneusta, at the beginning of the branchial region, and the more posteriorly situated 

 coelomic spaces belong to the metasome, which by a secondary .segmentation has given rise 

 to the remainder of the myotomes. The collar-canals of the Hemichordata are represented in 

 Amphio.xus by the first pair of nephridial tubules, which open from the epipterj'gial cavities 

 (— parts of the collar-cavities) into the atrium. 



Van Wijhe thus definitely recognises the affinity of the Hemichordata to Amphio.xus. 

 The latter is indeed placed, with the Tunicata and the Craniata ("Craniota") in the Chordata; 

 while the Enteropneusta and Cephalodisats, constituting the Pharyngotremata, are associated, 

 with Rhabdopleura and Phoronis (to which no group-name is assigned) as Prochordata. But 

 he carries the comparison even further than has been done by most morphologists, since he 

 considers (p. 69) that the protocoel, mesocoels and metacoels can be identified in the embryos 

 of Petromyzon, Elasmobranchs and even in the higher Craniata, while (p. 70 n.) a proboscis- 

 pore can be recognised in the embryos of Elasmobranchs. 



It appears to me that a critical examination of van Wijhe's views can onl)- be made 

 as the result of an independent investigation of Amphioxus; but there are nevertheless one or 

 two points on which I should like to comment. The account of the collar-cavities is undoubtedly 

 of interest, confirming as it does the general accuracy of MacBride's observations on the 

 development of Amphroxus. Fig. 27, 28, and 32, given by van Wijhe, are specially significant 

 in shewing the existence, in the adult Amphioxus, of a well marked transverse septum between 

 the collar-cavities and those of the metasome. The prolongation of the outer lip-cavity into the 

 oral cirri may indicate that the floor of the buccal cavity corresponds with part of the operculum 

 in Ccphalodiscus, while somewhat further back the collar-cavity is .subdivided by a ventral 

 mesentery (cf. figs. 9 — 18), as in the same animal. The backward extension of this region of 

 the collar, on the ventral side of the pharynx, is also suggestive. Thus van Wijhe's fig. 1 5 

 represents an arrangement which is similar to what may be seen in sections of Cephalodiscus 

 transverse to the long axis of the zooid, in which the meta.somatic cavities occupy the dorsal 

 part of the section, while the collar-cavities still appear on the ventral side, subdivided by a 

 median mesentery. Taking this into consideration with H.\tschek's figs. 50 — 52 (81) of an embryo, 

 there is a remarkable similarity between the collar-cavities of Cephalodiscics and Amphioxus, 

 the coelomic sac in both cases having a triangular form when .seen from the side, the dorsal 

 j)art being much longer than the ventral part. While in Cephalodiscus the elongated dorsal 

 region of the collar-cavitv is connected with the arms, the anterior parts of the same region in 

 Amphioxus are cut off to form the lateral praeoral cavities ("Schnauzenhohlen") of van Wijhe. 

 The relations of the collar-cavities of the larval Amphioxus to the notochord and to the ventral 



