128 BULLETIN OF THE 



(Fig. 15) it is seen that a narrow slit-like diverticulum of the vestibule 

 passes behind the epistome. This diverticulum, which remains in very 

 much the same condition throughout life, does not give rise in toto to 

 the ganglion, which is merely formed by a differentiation of some of its 

 ectodermic cells." Harmer further doubts Hatschek's account of the 

 formation of the ganglion in Pedicellina, and believes that the lumen of 

 Hatschek's hollow sac is in reality the commencement of the fibrous 

 tissue which occupies the centre of the ganglion in the adult, and 

 which in optical sections might easily be mistaken for an empty space. 

 "Similarly," he continues, "Nitsehehas described the ganglion of Alcyo- 

 nella as originating as a diverticulum from the tentacle sheath. I regard 

 it as probable that the explanation which I have suggested for Pedicel- 

 Una will hold also for Alcyonella." The conditions which every student 

 of the embryology of Phylactolsemata has stated since MetschnikofFs 

 paper in 1871, and which my own results reaffirm, do not warrant Har- 

 mer's conclusions. The nerve fibres are very evident in the adult ganglion 

 of Cristatella, and in addition to them there is a cavity, ontogenetically 

 derived from the atrium, which, as SaefFtigen ('88, p. 96) has also 

 shown for Phylactolsemata, contains no histological elements (Plate V. 

 Fig. 52). 



6. Origin of the Funiculus and Muscles. — The origin of the so-called 

 funicular tissue in Gymnolaemata has been described already (page 126). 

 This same tissue also gives rise, according to Vigelius ('84, pp. 34, 35) 

 and others, to the retractor muscles of the polypide. As I have already 

 shown (pages 115-117, Figs. 22, 54), in writing of the origin of these 

 tissues in Cristatella, the ccelomic epithelium gives off cells, some of 

 which take on an amoeboid appearance, and, uniting together, form that 

 end of the funiculus which is attached to* the colony-wall. Other cells 

 from the ccelomic epithelium pass directly to the adjacent outer layer of 

 the bud, to form the nascent retractor and rotator muscles. Both of these 

 organs are, however, formed in part from cells composing the outer 

 layer of the bud, — itself closely related ontogenetically to the ccelomic 

 epithelium. 



These facts would seem to confirm the conclusion which the similar 

 relation of the two layers would suggest, namely, that the ccelomic 

 epithelium of Phylactolsemata is the homologue of the " endosarc " of 

 Gymnolaemata. 



