1909] Ritter: Halocynthia johnsoni n. sp. 75 



morphological and their taxonomic significance, from that in 



which they s1 1 before. It is clear now that in probably all 



aseidians with ;i highly complicated branchial membrane this 

 organ can be interpreted with confidence only by following its 

 developmental stages back to ;it least the full set of protostig- 

 mata of the embryo, and further, that a reference to the number 

 of stigmata and the different size-orders of transverse sinuses 

 without taking into account the size of the individual, can have 

 only a general value for species determination. 



As the present study falls much short of the larval stage I 

 am not prepared to discuss the sac makeup in any full- 

 ness. A few tacts have, however, been ascertained that will 

 be useful as a starting point for the study of earlier stages. Plate 

 13, tit;'. 15, is from a small individual. 1.25cm. and tit;-. 16 is 

 from an individual •"> cm. long. Both are intended to take in all 

 the sizes of transverse sinuses present in the sacs concerned. It 

 will he seen that four sizes occur in the smaller individual and 



six in the larger, and that in both the smallest are still in< - 



plete. It will also he seen that the stigmata are fewer in number 

 between the longitudinal vessels in tit;. 1."). and further that the 

 ratio of breadth to Length of the individual stigmata is greater 

 in the former figure, i.e., in the smaller individual. Although 

 I have not studied in detail either sinus or stigmata production, 

 1 may say that nothing appears contrary to the conclusions 

 reached by the authors above cited as well as by others, that new 

 stigmata are always produced from old ones. In view of this 

 apparently universal rule of stigmata production, it is interesting 

 to inquire whether new sinuses are also produced from old ones. 

 That such is not the case is almost certain, as the beginning 

 sinuses in both the figures here referred to indicate. 



4. Some Statistics on Variation. 



Tallies I and II present the quantitative results of the exam- 

 ination of twenty-five individuals of //. johnsoni. The series of 

 outline figures, 1 to 29, PI. 10, show the hypophysis mouth, and 

 the anus respectively, of these same individuals. 



