ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA — 337 
There is no distinct epidermic layer on either face of the test. 
‘The corpuscles are, as usual, stained dark yellowish brown by iodine ; 
while the matrix yields, though weakly, the characteristic reaction of 
cellulose. 
§ 3. Zhe Agamogenesis by Gemimation of PYROSOMA GIGANTEUM, 
Throughout the whole extent of the ascidiarium, the number of 
ascidiozooids appears to be undergoing a constant increase, by the 
development of buds from those which already exist ; at least, I have 
not yet met with any adult ascidiozooids devoid of a more or less 
advanced appendage of this kind. Gemmation always takes place 
from that part of the middle of the hemal side of the’ body of the 
-ascidiozooid, which lies opposite the bend of the intestine and between 
the posterior extremity of the endostyle and the reproductive organs. 
At first, therefore, the bud is situated near the posterior or cloacal end 
of the body, and on the same side as the closed apex of the ascidiarium. 
Gemmation does not take place in Pyrosomma, as in so many of the 
lower animals (e.g. the Hydrozoa and Polysea, or Salpa and Clavelina 
among the Ascidians), by the outgrowth of a process of the body-wall 
whose primarily wholly indifferent parietes become differentiated into 
the organs of the bud, but, from the first, several components, derived 
from as many distinct parts of the parental organism, are distinguish- 
able in it, and each component is the source of certain parts of the 
new being, and of these only. Thus the body-wall or external tunic 
of the parent gives rise to the external tunic of the bud; while a 
process of the endostylic cone of the parent is evolved into the 
alimentary tract of the bud, and the reproductive organs of the latter 
are furnished by a part of that tissue whence the reproductive organs 
of the parent took their origin. 
Pl. XXX. [Plate 29] fig. 14 represents the condition of what I may 
term the gemmiparous region of the body in a young ascidiozooid, in 
which no distinct trace of a bud is discernible externally. The outer 
tunic, it will be observed, passes evenly backwards, and has the same 
structure in the situation of the future bud as elsewhere. The 
endostyle is continued upwards and backwards asa cellular cord, which 
contains a cavity continuous with the groove of the endostyle, is about 
zeoth of an inch thick, and is rounded-off at itsextremity. From this ° 
a thin sheet of indifferent tissue is continued downwards and back- 
wards, so that its plane forms nearly a right angle with the direction 
of the end of the endostyle, and suddenly thickens to -15th of an 
‘inch. After this it tapers off gradually to its extremity, which lies 
VOL. II Z 
