344 BULLETIN OF THE 



and an egg-bearing male produced by budding. The series could not 

 be still further reduced to one, for at the period when it had been use- 

 ful it had been made subservient to reproduction by eggs, and this 

 necessity for throwing off the eggs into the bodies off new zooids still 

 existing, one generation of buds must be formed to contain them. 



This " syncopation of development " leads to a diminution in the 

 number of egg-producing zooids, and however advantageous it might 

 be in other respects, it would lead to the diminution and final extinc- 

 tion of the species, unless the number of eggs discharged from each 

 ovary could be in some way increased. If the solitary salpa produced 

 but one bud at a time, only one egg at a time could be placed under 

 the conditions necessary for development, and of course, the number 

 of new embryos hatched during a given period would be only a little 

 more than one tenth as great as at that time when there were ten 

 egg-producing zooids in the series ; and in order to allow the syncopa- 

 tion to take place, the number of egg-bearing buds produced by each 

 egg-producing zooid must increase inversely as the number of the latter 

 in the series is diminished. Although most Tunicata produce only a 

 single bud at a time, some, as Amauricium, form a long tube which 

 divides up into a series of five or six buds, which develop simultane- 

 ously;* and in Pyrosoma, the Cyathozooid forms a stolon almost 

 exactly like that of Salpa, and this becomes constricted so as to form 

 a chain of four Ascidiozooids.t If, as there seems to be so much 

 reason to suppose, Salpa has been derived through a form like Dolio- 

 lum, from one similar to Pyrosoma, it must have begun its solitary 

 life with a tendency to produce several buds»nd thus set free several 

 eggs at a time ; and we can readily understand that, as the series 

 was shortened, and it became necessary for the eggs to be discharged 

 more rapidly, this stolon might lengthen, and thus give rise to a 

 greater number of eggs at once. This would demand that, in some 

 way, a supply of nutriment should be provided to supply the mate- 

 rial used in their formation, and since the number of males would 

 now greatly exceed that of the hermaphrodites the fertilization of 

 the eggs would now be amply provided for, and the development 

 of the testis of the egg-producing form would no longer be necessary. 

 As this does not develop until late in life, it would exist, during the 



* Kowalevsky. Knospung der Ascidian. 



t Kowalevsky. Entwickelung der Pyrosoma. 



