56 BULLETIN OF THE 



layer are columnar and full of granular protoplasm, the mesodermal cells 

 cuboid. The body wall has clearly begun to invaginate in this I'egion. 

 Figure 79 is a similar section, and shows a later stage in this process. 

 The lumen of the bud is apparent, and has been formed by invagination, 

 not, as in Paludicella or Phylactolsemata, by ingression. The two layers 

 of the bud are apparent; they have been derived from those of tlie 

 body wall. 



Figure 73 (Plate IX.) shows a stage in the development of the poly- 

 pide which is intermediate between that of Figures 75 and 79, but from 

 another suborder, Cheilostomata. The mesoderm has here a mesenchym- 

 atous character, and is loosely attached to the inner hiyer of the bud ; it 

 is not always sharply marked off from it by boundaries, but is quite dis- 

 tinct in its reaction with staining reagents. This bud has evidently 

 arisen by invagination of the body wall. Seeliger ('90, p. 581) also finds 

 that there is an actual invagination of the ectoderm in Bugula, the open- 

 ing to which he calls " blastopore." 



From what has been already shown, it is evident that in Flustrella, as 

 well as in Cheilostomata, the first appearance of the young polypide is 

 near the margin of the stock, not near the proximal part of the young 

 zooecium. This will also be apparent at 6 and 9, Figure 71 (Plate VIII.), 

 where the accumulation of nuclei immediately behind the margin indi- 

 cates the neck of the polypide, — the point at which the bud arose. To 

 be sure, at quite an early stage, but very much later than that of Figure 

 73, the polypides are found near the proximal wall of the zooecium, but 

 a delicate funnel-shaped sheath of tissue runs from the polypide to the 

 distal part of the zooecium, where the polypide is attached to the body 

 wall. 



After invagination the pocket closes at its attached end by a growing 

 together of its lips (Figs. 79, 78). Thus the body wall becomes contin- 

 uous again over the lumen of the bud, and this union is first broken 

 when the fully formed polypide is ready to evaginate itself. Seeliger 

 ('90, p. 582, Taf. XXVI. Figs. 8, 10) has described and figured a similar 

 condition in Bugula. 



The young bud now becomes elongated (Fig. 80), the walls of the bud 

 sometimes becoming closely approximated. A little later it begins to 

 pass backwards relatively to the distal wall of the zooecium. A trans- 

 verse section through the young polypide and the neck of the colony 

 shows that the connection has become a less intimate one (Fig. 81, cev. 

 pycL). The tissue by which the connection is still effected is that from 

 which the kamptoderm will be formed. It is apparently the existence 



