ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
29 
without the formation of a cavity. The distal part of the bud, in which 
the alimentary tract is to arise, is formed by a rapid growth of the walls 
of the bud. As this rapid growth occurs earlier at the anal side than 
at tho oral, the rectum is formed first and the stomach last. The 
alimentary tract and atrio-pharyngeal cavity become separated by an 
approximation of the lateral walls. The oesophagus arises as a pocket 
of the cavity, and forms a secondary union with the stomach. 
The lophophore first arises in the form of two lateral thickenings of 
the atrio-pharyngeal wall, then as two lateral folds, the cavity of which 
becomes the ring-canal. Tentacles appear on the ridge of the lopho- 
phoric fold ; the posterior end of the fold is the last to be formed, and, 
in forming, it cuts otf the anal part of the atrium from the intertenta- 
cular cavity ; this last, which is at first compressed, becomes circular by 
change in position of the oral tentacles. The ganglion arises as a 
depression in the floor of the intertentacular space and becomes imbedded 
in the pharynx, which is differentiated by the change in position of the 
oral tentacles. Muscles and funiculi arise from tho cceloinic epithelium 
of both the body-wall and the bud. The neck of the polypide may sink 
to a considerable distance below the general level of the body, and form 
the marginal ridge of the Phylactoloemata and the diaphragm of the 
Gymnoloemata. The atrial opening first arises, at a late period, by 
separation of the cells of the neck. 
The communication plate arises in PaludiceJla as a circular fold of 
the layers of the body-wall, the mesodermal cells at tho centre of which 
become cuticularized. The mesodermal cells of this form become stored 
with food-material before the formation of the communication plate, and 
yield it up to the rapidly growing bud. The regenerated, like the 
mai’ginal, polypides arise in the Cheilostomata at a definite position, 
viz. on the wall of the operculum, from tissue left behind to give rise to 
the polypides, but not wholly used up in its formation. They arise 
wholly from the body-wall, come to lie next to the “ brown body,” and 
cause its disintegration. 
The author sums up his more important theoretical conclusions in 
the following terms : — There is in every stock or corm of Bryozoa a 
mass of inditferent cell-material, which is derived directly from the 
indifferent cells of the larva or embryo, and which has the function of 
forming the organs of the different individuals, including the polypides. 
This mass, by constant growth and division, affords the embryonic 
material for lateral branches. The form of the stock and interrelation 
of individuals is largely controlled by food-supply. 
The inner layer of the Phylactoloematous larva represents mesoderm 
only ; the endoderm has become vestigial through loss of the alimen- 
tary function. The polypides arise in Phylactoloemata at the pole 
of ingression, which is probably homologous with the aboral pole of 
Gymnoloemata. The inner layer of the polypide bud is composed of 
cells derived from the rim of the blastopore, and they are to be regarded 
as still indifferent, and as first becoming differentiated into ectoderm 
and endoderm in the formation of the young polypide. Gemmiparous 
tissue is a rapidly assimilating tissue possessing large nuclei, because 
actively assimilating, and staining deeply because full of food material. 
The larvae of the Eudoprocta and Ectoprocta are to be compared by 
