tions are possibly to be regarded as ho.'nologous \7ith the epi- 

 cardial sacs of some other Ascidians. 



4. The endostyle appears early as a longitudinal 

 groove in the middle of the thickened portion of the vesicle; 

 from its primitive position on the ri^ht side it is moved 

 dov/n to tne ventral mid-line by thp displacement of the ves- 

 icle. 



5. The digestive tract grows out laterally as a 

 blind tube from the posterior end of the inner vesicle high 

 up on the left side. During the change in position of the 

 vesicle, its opening into the latter is carried up into the 

 median plane. 



The "organe refringent" arises as a tubular diver- 

 ticulim from the anterior face of the stomach, and produces 

 a dichotomously branched system of tubules, which surround 

 the intestine and terminate in little dilated vesicles or am- 

 pullae . 



6. All the evidence goes to show that the peri- 

 cardium is formed from free meso.iernal cells. It first ap- 

 pears as a clump of cells adhering to the outer surface of 

 the inner vesicle far wp on the right side, and through the 

 shifting of the vesicle is brought down to the ventral side. 



7. The dorsal tube and ganglion are formed only 

 in part from a common rudiment, and there is every reason to 

 believe tnat both are derived solely from tne mesoderm. The 

 former appears as an elongated, solid mass of cells, which 

 lies close against the outer surface of the inner vesicle, 



