80 University of Calif ornia Publications in Zoology. [Vol.6 



With attention focused upon the multiplication of parts in 

 the branchial sac. as it is primarily by the studies of the French 

 naturalists, and upon a similar process in tentacle development 

 by the present study; and further upon the wide prevalence of 

 a more or less distinct numerical order in the general make-up 

 of the ascidian body clear to every zoologist, various far-reaching 

 biological questions come easily to the front. 1. To what extent 

 should the individual ascidian 6< looked nin-n as a compositt of 

 mort in- less indi /« ml< nl systt ms or parts, each growing and mul- 

 tiplying in ils own trail, i.i . in iicrnrihnici with ils men particular 

 nature? Ft is easy to give this general question objectivity in 

 tin- case of such a species as Halocynthia johnsoni. See the sys- 

 tems, or parts that are describable, numerable and of irse for 



some portion of the individual's lifetime arc increasing in num- 

 ber by one means or another: the mantle musculature, particu- 

 larly the radial siphonal muscles (fig. 2): Hie gonadial lobes 

 Bgs. - and 3), (to say nothing of the ovarian and testicular 

 lobes proper contained in the larger lobes), and the lobes aboul 

 t he opening of the oviduct and sperm duet i fig. 5 ) : in connection 

 with the digestive tract the branched and alveolated liver I fig. 4), 

 tlie lobulated lacteal system (figs. 3 and (>). and the anal lobes 

 (ti.e-. 7) : in the branchial apparatus the circlet of branchial ten- 

 tacles each with its branches primary, secondary and tertiary 

 (figs. 11-13); and finally the branchial folds, the stigmata, the 

 branchial vessels or similes longitudinal and transverse, and the 

 dorsal languets (ties. 14 and 16). In the face of such an array 

 of repetitive structures, several of which have already revealed 

 to cursory inspection a certain amount of "law and order." the 

 question can hardly be avoided. Is it not likely that still closer, 

 mure detailed observation would discover still other repetitive 

 parts whose production is also reducible to law.' How docs the 

 problem before us differ from that of metamerism so much dis- 

 cussed a couple of decades ago? Is not that problem as it has 

 usually been treated merely a special aspeel of a much more 

 general problem, viz., that of the meristic constitution of the 



eiitii rganism? If this question is entitled to an affirmative 



answer, as it seems to me it is. it would appear doubtful if there 

 are any animals whatever, to say nothing of plants, that are not 



