MUSEUM OF COMPAEATIVE ZOOLOGY. 39 



That the nutritive matter iu tlie coelomic cells is supplied to the 

 young bud is what we should expect, since the cells of the bud, being 

 most actively engaged in growth, will require most nutriment. The 

 actively dividing cells of the outer layer of the bud are thick and cuboid, 

 and are rarely so highly vacuolated as the more passive ones of the body 

 wall ; yet occasionally one finds one or two huge cells in this layer full 

 of vacuoles, which contain highly refractive bodies. In most cases these 

 cells send out processes into the coeloni, and iu a few instances I have 

 seen them miited with similar processes from cells on distant parts 

 of the body wall. This remarkable phenomenon, shown in Figure 54 

 (Plate VI.), may possibly signify that cells of the coelomic epithelium at 

 times directly communicate with those of the outer layer of the bud to 

 supply it with nourishment. Nutrition of the bud is also probably 

 effected through the presence of large reticulated cells at the angle 

 between the bud and the body wall. A condition like that shown in 

 Figure 56, cl. ret., is very common. 



Every author from Dumortier et van Beneden to Braem, who has 

 studied the origin of the polypide in Paludicella, has mentioned the 

 presence of highly refractive bodies in the alimentary tract at the time of 

 its formation. These are very striking in some living specimens, and 

 in whole animals after killing. I have found that this highly refractive 

 substance in the bud is exceedingly variable in amount and position, 

 and that sometimes it is apparently absent. When present, it usually 

 occupies the lumen of the forming alimentary canal ; but, as sections 

 show, it is often located in large vacuoles in the future digestive cells 

 of the alimentary tract. It seems highly probable that, as Braem sug- 

 gests, this is nutritive substance, and it has doubtless come from the 

 body cavity through the agency not only of the outer layer of the bud, 

 but also of other parts of the coelomic epithelium. 



I am inclined to interpret the phenomenon of cells filled with nutri- 

 tive material as an adaptation to the peculiar conditions of Paludicella, 

 in which the individuals are early separated from one another, except 

 for the communication plate, through which at best fluids can pass only 

 slowly, and in which a rapid growth of the body wall to produce the 

 polypide takes place periodically. The mesodermal cells rapidly absorb 

 the nutritive fluids of the body cavity and store them in their substance 

 before the formation of the communication plate, and give them out 

 again during the period of the polypide's most rapid growth chiefly to 

 this part of the individual. This hypothesis has been mainly derived 

 from considering the fact of the great development of the reticulated 



