ON JULINIA. 3 



each system is a large and irregularly-lobed common cloacal 

 opening. 



In a transverse section through the colony (PI. 1, fig. 9) 

 the zooids are seen arranged round the circumference. From 

 their proximal ends vascular processes pass inwards, branching 

 and interlacing in the interior of the colony. In the further 

 structure of the framework of the colony we have to deal with 

 a number of elements more or less obscure, which may be 

 briefly enumerated but which remain here as in other cases 

 imperfectly understood. Just below the ascidiozooids large 

 numbers of peculiar vesicles occur scattered among the vessels. 

 These vesicles are spherical, from '3 to '7 mm. in diameter, and 

 consist of a denser layer of the test-substance surrounding a gra- 

 nular mass of variable size and appearance, in which numerous 

 nuclei are occasionally found. It is possible that these masses 

 may represent degenerating zooids like those described by 

 Maurice in Fragaroides, though their great abundance is 

 rather against this view. Many buds in diff'erent stages of 

 development occur scattered among these vesicles. The centre 

 or core of the colony is composed of the spongy test-substance, 

 traversed by the vascular processes, which here run more or less 

 in a longitudinal direction. 



In its minute structure the test resembles that described by 

 Herdman in Colella (1. c, p. 78). In section (PI. 3, fig. 32) 

 it presents a reticulate appearance, the cavities occupied by the 

 large vesicular or vacuolated cells known as " bladder-cells" 

 reducing the matrix to a mere interstitial network. These 

 " bladder-cells" are of common, but not universal occurrence 

 among Compound Ascidians. 



In the immediate neighbourhood of the zooids and of the 

 vascular processes the tissue is denser, forming tracts of homo- 

 ge)ieous matrix-substance which show, besides a few bladder- 

 cells, small test-cells of the more usual type, with scanty 

 protoplasm and irregular outline. Near the surface of the 

 colony numerous groups of yellowish pigment-cells occur. 

 These are irregularly rounded (probably shrivelled by the 

 spirit), highly refracting, and apparently homogeneous. In 



