1'2S BULLETIN OF THE 



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

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

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

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

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

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

 Hatschek's hollow sac is in reality the commencement of the fibi-ous 

 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, "Nitsche has described the ganglion of^lAv/o- 

 iLtlla as originating as a diverticulum from the tentacle sheath. 1 ix-gard 

 it as probable that the explanation whirh I have suggested iur raJicrl- 

 lina will hold also for Alci/onella" The conditions whicli every student 

 of the embryology of Phylactolccmata has stated since MetschnikoiFs 

 paper in 1871, and which my own residts reailii-m, do not warrant Ilar- 

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

 of Cristatella, and in addition to them there is a cavit}-, ontogenetically 

 derived frt)m the atrium, wliicli, as Saefftigen ('88, p. 9G) lias also 

 shown for I'hylactolaimata, contains no histological elements (Plate V. 

 Fig. 52). 



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

 funicular tissue in Gymnolajmata has been described already (page 12G). 

 This same tissue also gives rise, according to Vigelius ('81, p{). 34, 35) 

 and others, to the retractor muscles of the polypide. As 1 have already 

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

 tissues in Cristatella, the coelomic 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 coelomic epithelium jiass directh' 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 coelomic 

 epithelium. 



These facts would seem to confirm the conclusion which tlic similar 

 relation of the two layoi's would suggest, nameh', that the coelomic 

 epithelium of Phylactolamata is the homologue of the " endosarc " of 

 Gymnola^mata. 



