SPLEEN OF LEPIDOSIREN AND PROTOPTERUS. 
235 
that the spleen projects for most of its length, but the 
posterior end, where it continues to overlap the pancreas, is 
contained within it. 
The histology is as follows : The cells are arranged to form 
closely-packed trabeculae, surrounded by blood spaces. These 
have no endothelial lining, and are the venous sinuses pre- 
viously mentioned. The peripheral sinuses, which were so 
well marked in the earlier stages, are now completely broken 
up by trabeculae to form the channels of the sponge-work. 
The blood supply is rather doubtful. There appears to be 
a small branch of the coeliac artery actiug as an afferent 
vessel in addition to the branches of the intestinal vein ; but, 
I think, some of the blood from the intestinal goes direct to 
the liver. The factors of the Hepatic Portal Vein compose, 
as before, the efferent system. 
The Spleen of Lepidosiren. 
Turning now to the development of the spleen in Lepi- 
dosiren, the differences observable are not of much morpho- 
logical significance. 
It apnears at just about the same stage as in Protopterus, 
but develops rather more quickly, so that by Stage 34, 
(figs. 5 and 5a) it is aleady about 1 mm. long, and shows the 
beginnings of a trabecular arrangement among its cells. 
Its position, too, differs from that in Protopterus; it is 
dorsal to the foregut anteriorly, turning over to the right side 
posteriorly, and lies almost entirely in front of the intestine. 
This last point of contrast is due to the difference of distribu- 
tion of yolk in the two species. 
I have been unable to discover a branch of the coeliac 
artery supplying it, but the intestinal vein, besides supplying 
the spleen, does continue directly to the liver. 
Already, however, at Stage 35, a branch of the coeliac 
artery can be made out going to the spleen, which is as far 
developed as the latest stage of Protopterus that I have 
examined (figs. 6 and 6a). 
