100 BULLETIN OF THE 



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

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

 epithelium (Figs. 6, 28, 56). 



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

 similating tissue, j>ossessing 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 Knospuug der Bryozoen uns zeigen, wie histologisch sehr 

 bestimtnt diffei'enzirte Gewebe einen ganz embryonalen Charakter wie- 

 dergewinuen konuen. Mehr noch als bei der normalen Knospung am 

 freien Stockende ist dieses Vermogeu bei der Regeneration der Polypide 

 der Ektoprokten oder der Kopfchen der Pedicellinen ausgebildet. In 

 diesen Fallen sehen wir eiu plasmaarmes, ausserest feiues Plattenepithel, 

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

 und cylindrische plasmareiche Zellen zuriiekverwandeln 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 

 iu fiivor of Nussbaura'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 lajer 

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



1 Other observers describe gemmiparous tissue as being eitlier 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 runden 

 Kern und fiiliren Oel- und Fettsubstanzen die als Reservematerial beini 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 

 pharynx of dividing Microstoma : " Dieselben nehmen an Griisse zu, . . . indem 

 gleichzeitig ihre Protoplasmaleiber feinkurnig granulirt und fiir Farbstoffe imbibi- 

 tionsfaluger werden." 



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

 Dr. Wilson has very kindly sent me several slides, I find the outer laj'er 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. 



