REVIEW OF SPENGEL’S MONOGRAPH ON BALANOGLOSSUS. 391 
very narrow channel with the dorsal vessel, and by several 
chinks with the proboscis gland. The structure of the latter is 
explained in a beautifully lucid manner ; it consists of nothing 
but the posterior epithelial wall of the proboscis cavity, which is 
pushed forward into the cavity by the forward growth of the 
notochord. It is thrown into folds, to which correspond wide 
blood-vessels connected with each other in a net-like manner. 
The epithelium covering them consists of large pale cells with 
often concretions of yellow granules, probably excretory in 
nature. Blood is apparently carried from it by two lateral 
vessels, which run along the notochord to the buccal cavity. 
Here they run first obliquely and then vertically downward, 
and unite underneath the gut to form the ventral plexus 
of the collar region, which opens behind into the ventral 
vessel. 
The blood-supply of the gill-sacs is only part of the enteric 
plexus; it is specially richly developed around the inner open- 
ing of the gill-sacs, which appear to be their functionally 
active part. Special vessels arise from the dorsal vessel (see 
fig. 2) to join this network. 
The blood is a coagulable fluid, and contains abundance of 
those wandering cells or amcebocytes which are found in all 
Metazoa, from the medusa to man inclusive. In Ptychodera, 
the most differentiated genus, they appear to have given rise 
to a continuous endothelium in the larger vessels, but no trace 
of this is seen in the more primitive species. 
The skeletal system next claims our attention. There is 
no cuticle in the Enteropneusta; the entire surface of the skin 
(with the exception of discharging gland-cells) is ciliated, and 
the same remark applies to the gut-cells. The cells lining the 
U-shaped inner openings of the gill-sacs have powerful cilia. 
The Enteropneusta, however, unlike all Annelids and Arthro- 
pods, possess to a great extent the power of secreting cuticular 
or “ ground”’ substance from the inner or basal ends of the cells 
composing the various epithelia. Spengel calls this substance 
from the pericardium; but, as appears from his own description, similar 
remarks apply to the whole of the vascular system, 
