io6 



TUNICATA SALPIANS 



CHAP. 



"■5'-, 



«.Zi£-pH~J 



end 



really belongs to the solitary stolon-bearing Salpa, which is 

 therefore a female producing a series of males by asexual 

 gemmation, and depositing in each of these an ovum, which will 

 afterwards, when fertilised, develop in the body of the male into 

 a solitary or female Salpa. This idea, if adopted, would pro- 

 foundly modify our conception of SaljM as an example of a life- 

 history showing alternation of generations, but it seems to me to 



give a distorted view of the 

 sequence of events. The 

 fact that the stolon while' 

 in the solitary Salpa con- 

 tains, along with representa- 

 tives of other important 

 systems of the body, a row 

 of germinal cells, does not 

 constitute that solitary 

 Salpa the parent of the ova 

 which these germinal cells 

 will afterwards become in 

 the body of an independent 

 bud. We must regard as 

 the parent the body in 

 which the ova become 

 mature and fulfil their func- 

 tion. The sexual or chain 

 Salpa, although really her- 

 maphrodite in its life-his- 

 tory, is usually ^ proto- 

 gynous, i.e. the ova mature 

 at an earlier period than 

 the male organ or testis. 

 The ovum is presumably fertil- 



FlG. 66. — Salpa hexagona, Q. and G. Chain 

 form dissected from the left side, a, Anus ; 

 at, atrial aperture ; br, branchial aperture ; 

 d.l, dorsal lamina ("gill"); d.t, dorsal 

 tubercle ; emb, embryos ; end, endostyle ; 

 m.b 2, vi.b 7, second and seventh muscle- 

 bands ; ii.ff, nerve - ganglion ; v, visceral 

 " nucleus." (After Traustedt. ) 



This prevents self-fertilisation. 



ised by the spermatozoa of an older Salpa belonging to another 



chain, and the embryo is far advanced in its development before 



the testis is formed. The development takes place inside the 



body of the parent, and is " direct " — no tailed larval form being 



produced. 



Development and Life-history. — The segmentation of the 

 egg is holoblastic, and gives rise to a number of blastomeres, 



' According to Metcalf, Salpa cylindrica is protandrous. 



