and deepenirig rapidly in this region, gradually extends pos- 

 teriorly. 



As these changes are going on, the connection with 

 the stolonic partition is gradually becoming co: stricted, and 

 is now only present in the posterior half of the bud, while 

 at the same time the ectodermal stalk is also getting narrov/- 

 er. Ritter (24) in a preliminary note on the budding of Pe - 

 rophora, says that, "When the differentiation of tne 'endo- 



derm' into the branchial and two peribranchial sacs, takes 



tnat the de\/elopJng- 

 place, it does so in such a way blastozooid is connected v/ith 



the double walled partition of the stolon, not by the bran- 

 chial sac, as has been hitherto supposed, but by the left pe- 

 ribranchial sac." He does not, however, describe how this 

 comes about. Prom an examination cf Pigs. 10 and 11, it is 

 readily understood. The communication of the body-cavity of 

 the bud with the blood spaces of the stolon is never complete- 

 ly closed, as there is always a free circulation of blood 

 from the one to the other, but eventually the left peribran- 

 chial cavity is entirely severed from the stolonic partition. 



I cannot, hov/ever, confirm Ritter 's statement (I.e., page 

 367), that this connection is lost at an early stage, namely, 

 "at a time v/hen the two peribranchial pouches have merely be- 

 gun to envelop the branchial sac." I find that it persists 

 for a very much longer time, and is still present, although 

 greatly constricted, at a stage when some of the gill-slits 

 have been formed and the peribranchial cavity has been wholly 

 separated from the brancnial sac. Pig. 21, shov/s the con- 



•19- 



