MUSEUM OF COMPAKATIVE ZOOLOGY, 57 



of this stage, in which the kamptoderm. is long drawn out and easily 

 overlooked iu optical as well as actual sections, that led to the belief that 

 polypide buds may arise independently of the body wall and only sec- 

 ondarily become connected with it. 



At about this time the lumen of the alimentary tract begins to be 

 separated from that of the atrium. Thus, in the series from which Fig- 

 ure 81 was taken the more oral ward lying sections show that the cavities 

 of the lower and the upper parts of the bud, which at the anal end are 

 broadly confluent, have here become separated by a constriction. A 

 sagittal section of a somewhat later stage is shown in Figure 76, which 

 is from Flustrella. Here we find the alimentary tract represented by a 

 space in the lower part of the bud, broader at its anal than at its oral 

 end and separated from the upper cavity — the common atrio-pharyngeal 

 cavity, oe. + atr. — by a line of nuclei which represents the line of ap- 

 proximation of the inner layers of the two sides of the bud. The bud is 

 attached to the body wall at its marginal (anal) end, and is free from it 

 oralwards. (Compare with Paludicella, Plate III. Fig. 24.) It seems 

 to me highly probable from these and other series of sections that the 

 alimentary tract is separated from the rest of the lumen of the bud, not 

 by an approximation of the inner layers of the bud along the whole ex- 

 tent of the future alimentary tract at once, but that the rectal part is 

 first formed and constitutes a large cavity, at first broadly open to the 

 atrium above, and that the gastric portion is formed somewhat later by 

 a progressive enlargement of the lower cavity of the bud, which now 

 becomes constricted off from the atrium and oesophagus above. This 

 process is like that found in Paludicella (page 19), which forms a sort 

 of transition to that of Phylactolaemata, described by Braem ('90, pp. 

 45, 46) and myself ('90, p. 112). 



Prouho ('90, p. 448, Fig. 6) shows that the rectum at first appears 

 as a blind sac open to the atrium at its posterior end, although later 

 this opening is greatly reduced. Hence in the Flustrella larva also the 

 space from which the lumen of the future rectum is to arise is formed 

 before that of the stomach, although this part of the alimentary tract 

 is the last to be cut off from the atrium. Seeliger ('90, p. 585) says 

 concerning the formation of the alimentary tract in Bugula : " Der ganze 

 Basaltheil des Polypids sich in der Mittelpartie durch zwei immer tiefer 

 werdende Furchen von dem vorderen abschniirt, wahrend er an zwei 

 Stellen, einer oberen imd einer unteren, mit ihm in Verbindung bleibt. 

 Die obere Verbindung entspricht dem Anus, die untei-e dem Mund." The 

 author here seems to imply that the whole alimentary tract is formed at 



