100 BULLETIN OF THE 



granules observed in the cells are food material is indicated by their 

 abundance in cells lying next to the reticulated cells of the coelomic 

 epithelium (Figs. 6, 28, 56). 



My conclusion, then, is this : Gemmiparous tissue is a rapidly as- 

 similating tissue, possessing large nuclei because actively assimilating, and 

 staining deeply because full of food material} 



While for Nussbaum, as already quoted (page 71), " indifferent cells" 

 are essential to the reproduction of individuals by non-sexual as well as 

 by sexual methods, Seeliger ('90, p. 59G) has concluded that " die Vor- 

 gange bei der Knospung der Bryozoen uns zeigen, wie liistologisch sehr 

 bestimmt differenzirte Gewebe eineu ganz embryonalen Charakter wie- 

 dergewinnen konuen. Mehr noch als bei der nornialen Knospung am 

 freien Stockende ist dieses Vermogen bei der Regeneration der Polypide 

 der Ektoprokten oder der Kopfchen der Pedicellinen ausgebildet. In 

 diesen Fallen sehen wir eiu plasmaarraes, aussei'est feines Plattenepithel, 

 das iiber sich eine machtige Cuticula ausgeschieden hat, sich in kubische 

 und cylindrische plasmareiche Zellen zuriickvervvandeln und durch eine 

 Einstiilpung ein neues Polypid bilden, in welchem schliesslich die man- 

 nigfachsten Gewebsformen vertreten sind." 



It seems to me that many facts in the budding of Bryozoa are strongly 

 in favor of Nussbaum's hypothesis. On this assumption, we can best 

 understand why in Cristatella there is not an invagination of the ecto- 

 derm, and why instead a stolon is formed in the embryo, which passes 

 along at the base of tlie ectoderm and at intervals gives rise to the 

 inner layer of the body wall. I believe it is because the outer layer 

 of the body becomes so rapidly differentiated by the secretion of the 



1 Other observers describe gemmiparous tissue as being either rich in food or 

 deeply staining. Seeliger ('85, p 588) speaks thus of the mesodermal gemmiparous 

 tissue in Salpa : "Die einzelnen Zellen sind grossblasig, enthalten einen rundcn 

 Kern und fiihren Gel- und Fettsubstanzen die als Reservematerial beim Aufbau 

 des embryonalen Leibes weiterhin in Verwendung gelangen." Von Wagner ('90, 

 p. 377) says of the indifferent cells which are being transformed into the new 

 pliarynx of dividing Microstoma : " Dieselben nelimen an Grosse zu, . . . indeni 

 gleichzeitig ihre Protoplasmaleiber feinkurnig granulirt und fiir Farbstoffe imbibi- 

 tionsfaiiiger werden." 



In some sections of gemmules of Esperella fibrexilis, H. V. Wilson, of which 

 Dr. Wilson has very kindly sent me several slides, I find tlie outer layer of young 

 gemmnles, in which the inner layer has been newly formed, stained very deeply. 

 Observed with a Zeiss Apochr. 4.0 mm., Ocs. 8 and 12, the cell contents are seen to 

 be evidently of two kinds, — light and deeply stained. The latter appearance is 

 due, in part at least, to small dark granules, which can be discerned without much 

 difficulty. 



