62 



PHYLUM TUNICATA (UBOCHORDA). 



The whole body is pervaded by a gelatinous substance without 

 nucleated elements (excepting in the tail), but traversed by fibres 

 which run from the ectoderm to the walls of the internal organs, 



FIG. 55.Fritillaria furcata (after Lankester). A, side view ; B, viewed as a transparent ob- 

 ject ; C, side view as transparency ; D, ventral view, a otocyst ; b sensory pit ; c dorsal 

 hood ; A nerve cord passing from the ganglion on the right side of the stomach to the tail, 

 where it forms a series of enlargements ; e stomach ; / ovary ; g testis ; h notochord ; i nerve 

 cord in tail ; k supposed myomere of tail ; I anus ; m heart ; n gill-aperture ; o endostyle ; p 

 mouth. 



and hollowed out along certain tracts to form blood spaces. 

 This absence or paucity of mesenchymatous elements is charac- 

 teristic and recalls a similar condition found in Balanoglossus and 

 Amphioxus. The blood-channels are without epithelial walls, 



