Kingsley.] 
448 
[March 15, 
adult ascidian, midway between the oral and atrial apertures. 
Five of the processes of the larva remain, but in a much re- 
duced condition in comparison with the body. Only four of these 
are shown in the drawing. The heart was beating and the blood 
could be seen with its curious alternating motion, but its course 
is not shown in the figure. 
Fig. 19 shows the same embryo a week later, but drawn to a 
larger scale. Here the rudiments of the branchial tentacles may be 
seen around the branchial rings, and the folds of the pharynx are 
more numerous and more pronounced. Two branchial clefts ( b . r.) 
are developed each margined with cilia and keeping up a con- 
stant current of water. From the base of the pharyngeal sac 
arises the oesophagus, which is still a cylindrical tube and is 
slightly constricted before it ends in the stomach. The stomach 
is nearly spherical and from it passes the intestine, which has a 
short but well marked enlargement at its anterior end, and a sec- 
ond longer but more gradual one near its termination. The anus 
is small and opens near the base of the atrium. The heart is also 
seen and near it the structure which Lucaze-Duthiers has called 
the “ organ of Bojanus of its structure and function, and whether 
it be homologous or even analogous with the organ so called in 
the Lamellibranches I have no facts to offer. I can, however, 
hardly consider that two as distinct types as the Mollusca aud 
the Tunicata (which I believe to be Vertebrates) should have an 
organ of this character common to both. It may be renal or 
depuratory in its function, but I cannot regard it as the homol- 
ogue of the organ of Bojanus of the Acephala. The “ endostyle ” 
is also shown. 
There is a certain interest in the foregoing observations, incom- 
plete as they are, since they show that in the genus Molgula two 
distinct types of development are pursued. Kupffer and Lacaze- 
Dutliiers have studied the development of species of this genus 
and their results are greatly different from those which I obtained, 
and they may even show that two distinct genera have been 
studied. Still the case is paralleled by the development of the 
species of the crustacean Gammarus where a large variation has 
been noticed. 
In the species studied by Lacaze-Duthiers the eggs undergo all 
their development outside the body ; in our species the develop- 
