MUSEUM OF COMPARATIVE ZOOLOGY. 139 



two layers of cells, both belonging to the outer layer of the bud, form the 

 " Verbindungsstrang des Ganglions mit dem Lophoderm " of Kraepe- 

 lin ('87, p. 63, Taf. II. Fig. 59, vs.). (See Plate V. Fig. 51, Plate VI. 

 Fig. 56, and Plate IX. Fig. 80,*.) This canal is the only one by which 

 communication between the body cavity and the cavity of the epistome 

 can occur. It may be called the epistomic canal (Plate V. Fig. 52, 

 Plate VIII. Fig. 72, can. e stm.). 



The epistome proper arises at the point where the epistomic canal 

 ends blindly, above and in front of the brain (Plate VIII. Fig. 73, Plate 

 IX. Fig. 77, e stm.) ; it is a pocket, the outer wall of which is contin- 

 uous on its under surface with the oesophageal epithelium, and on its 

 upper surface with the floor of the atrium. The growth of this organ 

 is disproportionately great after the first evagination of the polypide. 

 That part of its wall which is turned towards the alimentary tract is 

 then much thicker than the remaining part ; it forms the posterior wall 

 of the pharynx (Plate VIII. Fig. 72, e stm. ; compare Plate IX. Fig. 81). 

 Is the epistome innervated by fibres from the brain, as maintained by 

 Hyatt ('68, pp. 41-43) 1 I have not succeeded in finding such fibres, 

 and the conditions of the formation of the epistome, cut off as it is from 

 the brain at every point, make such a connection improbable. 



Allman ('56, Fig. 8, Plate XL) and Korotneff ('75, p. 371) have 

 shown for Paludicella, and Nitsche ('71, p. 44) has shown for Flustra, 

 that an epistome-like fold occurs at an early stage of development, but 

 is absent in the adult. Such an organ has been described by Allman 

 ('56, p. 56) and other observers in Pedicellina, and it is still more 

 prominent in Loxosoma, in which the relation of the epistome to the 

 body cavity is similar to that in the Phylactolaemata. 



The constant occurrence of this organ in the development of Bryozoa, 

 and its presence in so many aberrant genera which seem to be some- 

 what allied to this group, can only be interpreted, it seems to me, as 

 signifying that it is an ancient and morphologically important organ. 

 The manner of its development in Cristatella seems to throw very 

 little light, however, upon its significance ; it arises rather late, and 

 does not become of any considerable size until the atrial opening is 

 made. 



6. Development of the Alimentary Tract. — The later development and 

 histological differentiation of the alimentary tract have not been hereto- 

 fore carefully studied. 



At the stage at which we left the alimentary tract (Plate III. Fig. 19) 

 only two parts were clearly differentiated, the oesophagus and the intes- 



