266 INVERTEBRATE MORPHOLOGY. 



in which the digestive tract is represented by a yolk-laden 

 mass of tissue, having little resemblance, however, to the 

 differentiated eiidoderinal tube of Pedicellina. The occur- 

 rence of such forms, however, shows that the absence of the 

 tract in Jjugula, etc., is the result of progressive degeneration, 

 such larvae as those of Pedicellina and Cyphonautes represent- 

 ing the primitive condition more nearly than the remarkable 

 larva of JJugula. 



The transformation of the Ectoproctous larvae into the adult is even 

 more remarkable than that of Pedicellina. Fixation takes place by the 

 oral surface, the adhesive organ being evaginated for the purpose, and is 

 succeeded by a degeneration of the corona and pyriform body. In Cypho- 

 nautes the digestive system completely degenerates likewise, a new one 

 being formed later, the tissue in the neighborhood of the apical thickening 

 taking a prominent part in its formation. In those larvae which are desti- 

 tute of a digestive tract one, corresponding to the second one of Cyplio- 

 nautes, develops after fixation, likewise from the tissue of the apical thick- 

 ening. The exact method of this regeneration, for so it may be con- 

 sidered, can hardly be described here without leading to a recapitulation 

 of details too minute for the scope of this work. It may be remarked, 

 however, that the phenomena do not seem to merit the designation of an 

 alternation of generations, as might at first sight be supposed, but are 

 rather simply a metamorphosis the significance of which is at present 

 decidedly obscure. 



Budding of the Polyzoa. As already stated, colony formation by bud- 

 ding is a characteristic feature of the Polyzoa, Loxosoma alone not pre- 

 senting this method of growth, though like other forms it reproduces by 

 budding, the buds, however, separating at an early stage from the parent. 

 In the Endoprocta a stolon arises from near the point of fixation of the 

 primary individual which develops from the ovum, mesoderm tissue from 

 the stalk of this individual migrating into the stolon, but there is no pro- 

 longation into it of the parental endoderm. At a more or less definite part 

 of the stolon the ectodermal cells thicken and later on invaginate towards 

 the centre of the stolon. This invagination becomes surrounded by meso- 

 derm already present in the stolon, and later differentiates into two cavi- 

 ties, one of which retains connection with the exterior and forms the 

 vestibular chamber, from the walls of which the tentacles develop, while 

 the other becomes the digestive tract, its original connection with the ves- 

 tibular cavity becoming the anus, the mouth developing later as a depres- 

 sion of the floor of the vestibular cavity which joins the stomach. It 

 is interesting to note that from the ectodermal invagination the nervous 

 system as well as the digestive tract develops. 



In the Ectoprocta practically the same method obtains in the budding, 

 though the stolon is represented by the tip of a branch or even by the 



