450 



Mr. A. G. Huntsman. 



[Mar. 3, 



has compared the pharynx of Perophora with the anterior two-thirds of the 

 pharynx of Ciona. 



The Perophoridse differ, therefore, from the other Dictyobranchiat.es in 

 having only one primary protostigma instead of two. They are also peculiar 

 as to the method of origin of the second and third protostigmata or proto- 

 stigmatic rows as they should be called. It may be that this method is to be 

 compared with that in Holozoa [Distaplia] as maintained by Julin. 



In the Krikobrancbiates the process is much modified by the division into 

 definitive stigmata occurring before or at the time of perforation of the 

 protostigmata. This is foreshadowed in Perophora. In Clavelina the first 

 stage is that with two stigmata, which appear simultaneously. The manner 

 in which these stigmata are curved and also their subsequent behaviour 

 show that one is the reverse of the other. They are evidently homologous 

 with the two first stigmata of the Dictyobranchiate, as has been argued by 

 Julin and Damas. They are secondary protostigmata, representing one 

 primary. By equal subdivision and also by budding at the ends (these buds 

 perforate after separation) two rows of stigmata are formed. This is the 

 division into definitive stigmata. There is a tendency for this to occur 

 before perforation of the protostigmata. By a transverse division of all the 

 stigmata of a row the number of rows is doubled. The beginning of this 

 process is shown for Clavelina in the last stage in the figure. This is the 

 usual Ascidian method for increasing the number of rows during the later 

 stages of development. It occurs relatively early here, and we shall see that 

 it occurs still earlier an other Krikobranchiates. 



In the figured scheme of the development in Clavelina the hypothetical 

 processes occurring before perforation are the same as for the Dictyo- 

 branchiate with the addition of the tendency of the protostigmata to divide 

 into definitive stigmata before perforation. In Archiascidia, according to 

 Julin (19046), the development of the stigmata is essentially the same as 

 in Clavelina. It differs from the latter in the failure of the two primary 

 rows of stigmata to divide. 



Of the remaining Krikobranchiates that have been studied, Holozoa 

 [Distaplia] shows the simplest condition. This has been represented in the 

 lowest but one series of stages in the figure. Two stigmata appear simultane- 

 ously. They are evidently homologous with the two first in Clavelina, 

 although there is no very definite indication of one being the reverse of the 

 other. They are to be considered as two secondary protostigmata repre- 

 senting one primary. They elongate and divide dorsoventrally, and about 

 the same time four new stigmata perforate just below. By new perforations 

 on the ventral side, and at a later stage on the dorsal side as well, four 



