BUDDING IN TUNIC AT A. 47 



themselves for comparison with the paired cloacal or peri- 

 branchial canals of the primary ascidiozooids of Pyrosoma. 

 Uljanin's statements that the pharyngeal outgrowths give 

 rise partly to the genital glands, and that the cloacal out- 

 growths furnish the rudiments of the musculature and 

 nervous system of the bud, are, however, most improbable. 

 There is no inherent difficulty in the origin of the nervous 

 system from the cloacal outgrowths, since the cloaca of 

 Doliolum is an ectodermal structure ; but it is impossible to 

 believe, upon the strength of Uljanin's optical sections alone, 

 that a special pair of cloacal prolongations gives rise to the 

 musculature as well as the nervous system, especially as 

 both Grobben and Uljanin assure us that the stolon actually 

 contains a special mesodermal rudiment. Both authors trace 

 the development of the pericardium from this element, and 

 Grobben derives the general musculature from it also. It 

 is pardonable, therefore, if we refrain for the present from 

 assenting to Uljanin's discordant conclusions upon the fate 

 of the cloacal outgrowths. We cannot in this case apply the 

 same general considerations in support of a common origin 

 of nerve and muscle from the ectoderm that were originally 

 urged in favour of Kleinenberg's contention in the case of 

 Lopadorhynchus. Kleinenberg's views, I believe, have 

 failed to be confirmed, reasonable as was the position of their 

 author ; but the particular mode of origin described by 

 Uljanin in Doliolum is altogether unprecedented and 

 circuitous. Recent research, moreover, has shown con- 

 clusively in the case of Slilpa (Brooks and Korotneff), 

 Pyrosoma and Distaplia (Salensky) that the neural rod in 

 the stolons of these forms is a local differentiation of the 

 ectoderm at the base of the stolon ; and I am, therefore, 

 strongly inclined to believe that the neural rudiment in the 

 stolo prolifcr of Doliolum will also eventually be traced to 

 an early proliferation of the thickened ectoderm which marks 

 the site of the commencing stolon. 1 Criticism thus drives 

 us back from Uljanin's conclusions to the position pre- 

 viously occupied by Grobben as to the nature of the 



1 Grobben, taf. iv., fig. 22 ; Uljanin, taf. viii., figs. 4 and 5. 



