MUSEUM OF COMPARATIVE ZOOLOGY. 115 



above the cavity of the ganglion, and the one between the cavity of the 

 ganglion and the oesophagus. The outer layers of these three folds 

 respectively fuse immediately behind the oesophagus ; the inner layers 

 are constricted off, but without closing the neck of the sac. Conse- 

 quently the neck of the ganglionic sac, instead of opening into the 

 atrium, now abuts upon the inner cell-layer at the angle between the 

 floor of the atrium and the oesophagus. The lower layers of the hori- 

 zontal folds thus become the upper wall of the ganglion (Fig. 35, tct. 

 gn.) ; the upper layers form the new floor of the atrium (Fig. 73, 

 pam. atr.), which lies between the lophophore arms, is continuous with 

 its median walls, and passes over into the walls of the alimentary tract 

 both in front and behind. The outer layer of the young bud only 

 secondarily makes its way in between the upper and lower layers of 

 these folds. It ultimately takes the form of a double layer embracing 

 a space, which is the epistomic canal. (Plate VIII. Fig. 73, lu. gn., 

 Plate V. Fig. 52, lu. gn., can. e stm.) 



4. Origin of the Kamptoderm. — While the alimentary tract, lopho- 

 phore arms, and nervous system are being marked out in the lower por- 

 tion of the bud, these organs become farther removed from the wall of 

 the colony by an enlargement of the atrium to meet the demands of 

 the augmenting volume of the lophophore. Pari passu with this en- 

 largement of the atrium, its walls diminish in thickness (compare kmp. 

 drm., Fig. 73, Plate VIII., with Fig. 18, Plate III.). This is rather the 

 result of a failure of the cells to multiply in proportion as the area of 

 the wall increases, than of a decrease in the number of cells already 

 formed. Both the inner and outer cell-layers of the bud take part in 

 the formation of this wall, as is evident from the figures. The wall of 

 the atrium was called "tentacular sheath" by Allman ('56, p. 12) and 

 Nitsche, but Kraepelin ('87, p. 19) employs the name "kamptoderm" 

 for this structure. I prefer this term to "tentacular sheath," and have 

 employed it both on account of the reasons given by him and because it 

 may be easily inflected, whereas " tentacular sheath " may not. The 

 kamptoderm, then, is formed of the upper portion of the bud, and both 

 of its cell-layers are concerned in its formation and persist in the adult. 



5. Origin of the Funiculus and Muscles. — Nitsche ('75, pp. 353, 354) 

 did not see the origin of the funiculus, but states that it suddenly occurs 

 lying close along the oral side of the bud, to which one end is at- 

 tached. Its proximal end is fastened, he says, to the inner layer of the 

 colony-wall, and by the growth of the latter between the funiculus and 

 the neck of the bud this end retreats from the young polypide. Brnem 



