442 



Mr. A. G. Huntsman. 



[Mar. 3, 



the first and fifth. These may be called the protostigmata of the first order 

 or primary, using the term proposed by de Selys and Damas but in a some- 

 what different sense. They correspond to a certain extent with the " primary 

 gill slits " of Willey and the " fentes branchiales " of Julin (1904). This early 

 division of the stigmatic rudiment produces elements with a similar orientation. 

 When they elongate to form the protostigmata, their concave surfaces are 

 posterior. 



The subdivision of the two primary protostigmata produces four proto- 

 stigmata of the second order or secondary. They correspond in position with 

 the first, fourth, fifth, and sixth. The two members of each pair are oriented 

 differently, one being the reverse of the other. 



The process of subdivision is repeated in the case of the first pair, giving 

 four protostigmata of the third order or tertiary, namely, the first, second, 

 third and fourth. Here also of each pair one is the reverse of the other. 

 There are no Ascidians in which there has been shown to be further sub- 

 division to form new protostigmata. 



The protostigmata are formed in two ways. First, by simple subdivision ; 

 second, by modified subdivision, resulting in the intercalation of new 

 stigmata. By these same processes acting in the same order, the proto- 

 stigmata are converted into the rows of definitive stigmata of the adult. 

 Frequently the two processes are not altogether distinct. An intermediate, 

 method of subdivision may occur. 



The Protostigmatic Condition in the Various Groups. 



Julin and Damas have blazed the way for a comparison of the various 

 kinds of stigmatogenesis to be found in Ascidians. Both, however, have- 

 based their classifications on definite stages, and have more or less ignored 

 the differences in the process. 



Damas (1904) uses as a basis the final protostigmatic condition, and 

 divides the Tunicata into the Mono-, Di-, Tetra-, Hexa- and Poly-pro- 

 stigmata. The Ceesiridae [Molgulidse] are separated from the Tethyidaa 

 [Cynthiidae], Styelidae, etc., and placed with the Cionidre, Phallusiidse, etc. 

 And, as I shall show subsequently, some of the Tethyidas would have to be 

 placed in the Hexa- and others in the Poly-prostigmata. Damas also 

 places the Pyrosomatidse and Doliolidae with the Tethyidee, etc. These are 

 unnatural groupings. 



Julin (1904a) uses as a basis the number of stigmata that perforate 

 independently and calls them " fentes branchiales." He makes three distinct 

 groups : those with one pair of " fentes branchiales," those with two pairs, 

 and those with three pairs. To the first group belong the pelagic Tunicata,. 



