Students of the Oligochaeta are well aware of the fact that there is a great difference of opinion amongst various observers even with regard to the function of the calciferous glands. Michaelsen (6, 1895) holds strongly that the function of the calciferous glands is the absorption of nutriment, and he always designates them as ‘chyle-sacs’. The excretion of lime, according to him, is a secondary function. The main objection urged against his view is the situation of the calciferous glands, since they lie far forward, and the main digestive region, i.e. the intestine, lies behind them. But this objection does not hold in the case of the intestinal glands, since they lie just at the right place, a little behind the middle of the body where the typhlosole ends, and the gut still extends behind for another 107 to 127 segments. They lie, therefore, just in the region where the main work of digestion and absorption takes place.
That the glands open into the gut by as many as eighteen openings in five segments strongly indicates that their secretions are poured into the gut through these openings. The nature of the secretions seems to be tryptic, since ammo-acids were formed as products of digestion in the experiments made. Further, the greater part of the blood of the last portion of the intestine (107 to 127 segments) is collected and taken to these glands, where it permeates the substance of the gland through a sinusoid capillary network. The blood from the glands is collected again by the intestino-dorsals and taken to the dorsal vessel, the entire blood-supply of the glands resembling a hepatic portal system. These facts taken together with the demonstration of glycogen granules within the glandular cells strongly suggest that the intestinal glands are of the nature of a hepato-pancreas. The structure of the gland-cells themselves and the development of the glands further corroborate these conclusions.
The observations and conclusions arrived at may now be summarized:
1. The intestinal glands of Butyphoeus waltoni lie on the dorsal surface of the gut and extend as paired glands from segments 79 to 83. As the two glands of a pair are fused in the middle dorsal line and the glands of successive segments are connected, we should speak of it as one large gland ex-tending over five segments.
2. The gland forms the posterior boundary of the typhlosole of the gut, there being no typhlosole behind the region of the gland.
3. The gland is more or less solid and consists of lobules of glandular epithelium and interlacing lamellae. The lobules are separated from one another by sinusoid capillaries, while the two epithelial folds of a lamella enclose a blood-sinus between them.
4. The gland-cells are rhomboidal to polyhedral in outline, and their shape and structure strongly resemble those of livercells. They do not bear cilia or rodlets.
5. The whole gland opens into the gut through as many as eighteen apertures over five segments. These apertures are lined with the ciliated gut-epithelium.
6. The blood-supply of the gland resembles a hepatic portal system. The blood is collected from the gut of the last 107 to 127 segments into a ventral i n t e s t i n a l sinus which empties all its blood into the sinusoid capillaries of the gland. The capillaries of the gland join together to form five pairs of i n t e s t i n o - d o r s a l vessels which carry all the blood of the glands into the dorsal vessel.
7. The glands develop as dorsal outgrowths of the endodermal lining of the embryonic gut.
8. The glands secrete no calcium whatever. Calcified milk was curdled by the gland-extract in fourteen minutes. A tryptic enzyme has been demonstrated by the formation of amino-acids in digestion experiments.
9. Thickly set glycogen granules have been demonstrated by staining the gland-cells with Best's carmine.
10. The glands are, therefore, of the nature of a hepatopancreas.
The Blood-system in the Serpulimorpha (Annelida, Polychaeta)