132 BULLETIN OF THE 



development of the lophophore in Gymnolsemata. At a very early 

 stage, the rudiments of the tentacles, he says, are seen lying in a 

 U-shaped line, surrounding the mouth in front, but unclosed behind. 

 The same is true for Paludicella (Korotneff, '75, p. 371). The post- 

 oral tentacles make their appearance at the posterior free ends of the 

 row of tentacles. They are bent slightly downward, so as to be con- 

 cealed by the tentacles above. At a later stage, the tentacles lying 

 next to the anus gradually come to lie nearer to the anal side of the 

 mouth opening, the nearly parallel lateral rows lose their compressed 

 appearance, and a circular basin is formed whose walls are constituted 

 by the corona of tentacles. 



In Pedicellina (Hatschek, '77, pp. 520, 521) the tentacles arise as 

 five pairs of papilla-like processes in the upper part of the atrium. 

 Two additional pairs are formed later nearer the anal opening. In the 

 adult (Nitsche, 7 69, p. 21) the tentacles are arranged with bilateral 

 symmetry, and so that the plane of symmetry passes through two inter- 

 tentacular spaces, which are thus the only unpaired spaces ; they are 

 also much broader than the others. 



One might be inclined to ask by what modification of the condition 

 of the tentacles in Endoprocta we may suppose the condition in Ecto- 

 procta to have arisen, but the question is not a fair one. I have 

 already (page 127) shown that the young bud of Cristatella has many 

 points of similarity to a well advanced Endoproct. This similarity 

 leads me to the conclusion that the common ancestor of the Endo- 

 procta and Phylactokemata more nearly resembled the former than the 

 latter group. But the Endoprocta are not that common ancestor ; 

 rather they are themselves more or less modified descendants of it. 

 The proper inquiry is, To what ancestral relation between tentacles and 

 anal opening does a comparison of the ontogeny of Endoprocta and 

 Ectoprocta point, and by what modifications of that ancestral type may 

 the two divergent types of the present be derived 1 Eliminating for a 

 moment the evidently coenogenetic character of the lophophore arm, an 

 early stage of either Endoprocta or Ectoprocta reveals a U-shaped band 

 from which tentacles are to arise. This band completely encircles the 

 mouth, and passes posteriorly as far as the anus. This is the condition 

 of the Endoproct bud, with only five of its seven pairs of tentacles 

 formed ; it is also the condition of the Cristatella bud of Stage XIII. 

 (compare Figs. 19, 44). Starting from this common condition, that of 

 the adult Endoproct, on the one hand, was attained by the addition of 

 two pairs of tentacles posteriorly, thus nearly completing the circlet 



