98 



TUNICATA SALPIANS 



further division, to the sexual generation, which is polymorphic 

 — having three distinct forms, in two of which the repro- 

 ductive organs remain undeveloped. 



The primary huds are constricted off while still very young 

 and undeveloped (Fig. 60, D, B, and E) ; they migrate from their 

 place of origin on the stolon, over the surface (aided by large 

 amoeboid test-cells which become attached to the buds) (Fig. 60, 

 B), multiply by fission, and become attached (again by the help 

 of amoeboid test-cells and ectoderm cells which form a slight 



PiQ. 60. — Life-listory of Doliolum. A, tailed larval stage; B, "nurse" or oozoold, 

 showing buds (blastozooids) migrating from the ventral stolon to the dorsal process ; 

 C, posterior part of much later oozooid to show buds arranged in three rows on 

 dorsal process ; D, stolon segmenting ; E, young migrating bud ; F, trophozooid 

 developed from one of the buds of a lateral row. At, Atrial aperture ; 6, buds ; Br, 

 branchial aperture ; cl, cloaca ; d.p, dorsal process ; eiid, endostyle ; ht, heart ; /. h, 

 lateral buds; m.b, median buds; n,g, nerve - ganglion ; ot, otocyst ; ^.c, peri- 

 cardium ; sk, stalk ; sto, stolon. (After Uljauin and Barrois.) 



" placenta ") in three rows — a median and two lateral — to 

 the dorsal outgrowth (Fig. 60, C) of the body of the nurse. 

 This parent - form by this time has become greatly modified, 

 and its structure is largely sacrificed for the good of the buds or 

 growing zooids, for which it really forms a locomotory organ. 

 Its muscle-bands become greatly developed in width (Fig. 60, 

 C), and the branchial meshwork, endostyle, and alimentary canal 

 disappear. 



The three forms produced in the second generation are as 

 follows : — (1) Nutritive forms (" trophozooids ") derived from the 

 lateral rows of buds, which remain permanently attached to the 



