REPORT ON THE TUNICATA. 
blood-corpuscles, may possibly be regarded as suppljung the endodermal element to the 
bud. 
The Formation of the Colony . — It has already been stated that buds advanced in 
development are only met with in the upper part of the stalk, while at the very top the 
buds are almost in the condition of young Ascidiozooids (such as PL IX. fig. 12). These 
last form a perfectly graduated series with the young Ascidiozooids placed at the base of 
the head, showing very plainly that the latter are derived from stalk buds. All the 
middle part of the head is occupied by adult Ascidiozooids in full vigour, no young ones 
being found amongst them. In the upper part, on the other hand, it is evident that the 
colony is in a state of decay, gaps being found, and Ascidiozooids in a semi-decomposed 
condition occurring here and there, while at the very summit of the colony all is dead, 
no Ascidiozooids are present, and the investing mass is ragged and evidently wasting 
away (PL Y. fig. 2). 
All this suggests that the following is the probable method of increase and maintenance 
of the colony. After having been once established, by the development of a tailed larva, 
it grows from the lower part of the future stalk where the test substance or investing 
mass alone is produced. As this gets pushed up by the formation of more below it the 
end of a vascular appendage from the single Ascidiozooid in the head above penetrates 
down into it and in course of time produces one or more buds. These become imbedded 
in the investing mass around the vascular appendage, and proceed to develop, occupying, 
as they advance in age and size, successively higher and higher positions in the young 
stalk on account of the constant growth at the base of the colony. In this way, when 
fully developed, they reach the top of the stalk ready to take their places as young 
Ascidiozooids at the base of the head. 
In the fully developed colony the buds are produced near the centre of the stalk, 
while, when they reach the base of the head, they occupy the outer layer. This change 
in position is caused by their being jDushed outwards as they advance towards the head 
by the new vascular appendages which are constantly growing downwards from the young 
Ascidiozooids above them and wdiich occupy the centre of the stalk. Thus the buds are 
gradually forced into their peripheral position. 
After entering the head the young Ascidiozooids continue to grow and soon reach 
maturity, sending dowui their vascular appendages through the stalk to form new buds, 
and producing also tailed larvae from true ova fertilized by the sjoermatozoa of the older 
Ascidiozooids. Still they are constantly being pushed upwards, and finally, after having 
developed and lived through the entire length of the colony, they reach the summit as 
old Ascidiozooids, die, and drop off. 
In this way it is obvious that the colony when once established may be maintained ; 
while if, as must be the case at first, the production of buds is in excess of the death and 
decay at the summit, the colony will increase in size. 
