GERM CELLS OF COELENTERATES 17 



established that budding in Hydra and hydroids is a process of 

 evagination, but the work of Lang, Hadzi, and Tannreuther 

 suggests an earher acti\dty of the interstitial cells. Even if the 

 interstitial cells were entirely responsible for the formation of the 

 bud, proof would not be thereby constituted for the germinal 

 nature of these cells, for they are differentiating into nema- 

 tocysts throughout the life of Hydra. Also these same cells 

 transform directly into ganglion cells earlier in the life history. 



Medusae are sexual individuals and ordinarily reproduce only 

 by eggs and spermatozoa, but there are a considerable number 

 which undergo a process of asexual reproduction and form other 

 generations of medusae by budding. The budded medusae later 

 become mature and form sex cells just as do the parent medusae. 

 The author ('17) has given a detailed account of this secondary 

 budding of medusae and of germ-cell formation in Hybocodon 

 prolifer; the gonads are produced from the ectoderm of the wall 

 of the stomach, while the new medusae come from the tissues of 

 the base of the tentacle at the margin of the bell. In a critical 

 examination of these medusae no evidence was obtained of the 

 migration of germ cells from the old to the budding medusae, but 

 the new buds arose from both layers of cells in the tentacle after 

 these cells had undergone regressive changes and become embry- 

 onic. In Hybocodon the asexual budding is not influenced by 

 the formation of sex organs. Miiller ('08) is in error in believing 

 the two methods to be mutually exclusive, for C. W. Hargitt 

 ('02), Perkins ('04), and the author ('17) have recorded abundant 

 cases of the simultaneous presence of buds and gonads. 



A. Agassiz ('65), Haeckel ('79), C. W. Hargitt ('04), Mayer 

 ('10), and others have described many cases of asexual budding 

 in medusae. Such buds may be formed, a few at a time, or many 

 at a time ; a single generation of buds may be produced or many 

 generations; and many regions of the medusae may be concerned 

 in their formation. Haeckel describes the buds on the stomach 

 wall of tarsia gemmifera (S. siphonophora) (fig. 10), more than 

 twenty being present at one time and several generations being 

 produced; in different species of Cytaeis (fig. 14) enormous 

 numbers of medusae may be budded from the stomach wall at 



