452 



Mr. A. G. Huntsman. 



[Mar. 3, 



instead of three or more ; also in the fact that the first primary divides into 

 two secondary before perforation. The Dictyobranchia differ from the 

 Krikobranchia in that the first primary protostigma divides into four tertiary. 

 The Krikobranchia are peculiar in the great abbreviation of the development. 

 True protostigmata can scarcely be said to occur. They divide into definitive 

 stigmata before perforation. 



It might be pointed out that the division of the two secondary proto- 

 stigmata into four rows in Holozoa is not absolutely distinct from the division 

 of the two secondary into four tertiary in the Dictyobranchia. Perophora 

 exhibits an intermediate condition. A protostigma corresponds with a row 

 of definitive stigmata. The division of a protostigma corresponds with the 

 doubling of a row of definitive stigmata. Different methods are followed in 

 the two cases, since the condition of the element differs in the two cases. 



Summary. 



The genesis of, the stigmata affords a proper basis for an understanding of 

 the structure of the adult pharynx. A classification based upon the adult 

 structure and development of the pharynx shows marked agreement with 

 the current classification based upon the adult structure of the whole body. 



The absolute number of protostigmata in each form is not as good a basis 

 for classification as the number plus the method of formation. Important 

 differences in the method occm\ Passing from the Krikobranchia through 

 the Dictyobranchia and Ptychobranchia, a continuous increase in the 

 number of primary protostigmata and a decrease in their ability to subdivide 

 can be seen. 



Among the new genera studied may be noticed the following : — 

 Tethyidce [Cynthiidce]. 



Pyura. — The protostigmata develop in the same way as in Ccesira 

 [Molgula]. 



Tethyum. — The development is a modification of that in Ccesira. The 

 intercalated stigmata arise by abstrictions from the growing points of the 

 ventral ends of the first stigmata. 



Boltenia. — An indefinite number of protostigmata are formed, all arising 

 by perforation except the second and fourth, which are intercalated and are 

 formed by the process described for Tethyum. 

 " Styelidce. 



Stycla. — The protostigmatic condition is the same as for Boltenia. 

 Polycitoridm. 



Polycitor (Polycitqr). — Four rows of stigmata arise by independent 

 perforation. 



