340 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
—of which the two former remain connected, until a new bud is 
‘developed in the distal end of the peduncle, while the latter, now 
contained wholly within the bud, and separated from the others by a 
considerable interval, is itself divisible into three portions. The first 
of these is the ovum, or rather ovisac, larger and more distinct than 
in the last-mentioned stage; the second is that part of the blastema 
near this, which will become the testis, but which, at present, has no 
definite form; and the third is represented by a slender band of 
indifferent tissue continued up to the apex of the branchial sac (the 
future extremity of the endostylic cone), which is the generative 
blastema of the nascent ascidiozooid and will supply reproductive 
organs to its buds. The interspace between the branchial sac and the 
outer tunic of the bud is in free communication with the blood-sinus 
of the parent, by means of the interval between the endostylic cone 
cand the wall of the peduncle ; and, in fact, this interspace is itself the 
foundation of all the blood-sinuses of the bud. 
This is as much as can be clearly made out from the inspection ot 
side views of buds in this and earlier stages; but much additional 
information is to be gained from other views of similar buds. Fig. 26 
exemplifies the appearances yielded by a bud about ;},nd of an inch 
in diameter, when seen from above. 
The transverse section of the wide sac-like prolongation of the 
endostyle thus presented to the eye is four-sided; the lateral and 
posterior walls are concave, while the middle of the anterior wall is 
produced into a sort of fold; so that the contour of the sac may be 
compared to that of a crown. Masses of indifferent tissue fill the 
interspace between the concavity of the lateral wall of the sac and the 
sides of the external tunic, while the interval between the posterior 
wall and the hinder part of the external tunic is nearly filled up by 
the young ovisac. Fig. 27 represents an advance upon this condition, 
—the two principal changes to be noted being, first, the conversion of 
the lateral massés of indifferent tissue into hollow oval bodies 
containing a very small cavity, and, secondly, the prolongation of the 
posterior cornua of the alimentary sac. 
It is obvious that if either of these buds were viewed sideways, the 
middle fold of the anterior face of the sac would appear like an 
anterior thickening, while the posterior prolonged cornua would 
simulate a posterior enlargement, and the whole would closely 
resemble fig. 19; and it now becomes important to prove, by the 
study of more advanced stages, the nature of the sac, of its anterior 
median fold, of its posterior cornua, and afterwards of the lateral sacs. 
Fig. 28 represents a larger bud, which presents more of its anterior 
