1g01-1902.] Report of the Microscopical Section. 377 
disappears, being absorbed into the body or cast off in shreds; 
the notochord, which gave it rank among the vertebrata, is 
dissolved ; but its outer covering, called the test or tunic, is 
growing apace, and when it has reached its adult stage it looks 
more like a piece of inanimate cartilaginous matter than a 
living thing. 
The appearance of the adult Ascidia is something like a 
leathern bottle with two openings—one at the anterior end, 
called the branchial aperture, and the other a little way down 
on the dorsal side, called the atrial aperture. The margin of 
each of these apertures is divided into a number of small 
lobes, and the number of these is held to be a means of 
distinguishing species. In the species under consideration 
there are eight lobes on the margin of the branchial aperture 
and six on that of the atrial. As a nerve runs to each of 
these lobes from the nerve-ganglion or brain, they are the most 
sensitive part of the animal. This nerve-ganglion is a small 
mass of dark-coloured matter situate on the dorsal edge, mid- 
way between the branchial and atrial apertures. By a little 
delicate manipulation it can be laid bare, and the individual 
nerves traced almost to their endings. 
As has been said, the outside covering of the Ascidia is 
called the test or tunic——hence the name of the order, 
tunicata. This test, which is an excretion from the next 
inner layer called the ectoderm, is of a cartilaginous con- 
sistence, is easily cut with a knife, and when freed from 
extraneous matter is very transparent. It is traversed by 
numerous blood lacunz, the course of which can be easily 
discerned by the naked eye when a piece is held up to the 
light. The size of the specimens examined was from four to 
six inches. 
By removing carefully the one side of the test longitudin- 
ally the whole internal economy of the Ascidia is laid bare, 
and we can thus examine the separate’ parts and see their 
relation to each other. Next to the test is a delicate layer 
called the ectoderm, and inside the ectoderm is a thicker layer 
called the body-wall or mantle. This layer contains a large 
number of muscles running longitudinally and transversely, 
and thus forming a kind of network. The mantle surrounds 
the whole animal, with openings at the two apertures. 
