Fig. 384.-Section of the heart (c) and pericardial cells (pc, pc) from the posterior part of the heart of a fly: l, l, nests of leucocytes situated between the heart and pericardial cells.—From a microphotograph, after Kowalevsky.
Fig. 385.—Cross-section of the heart of Truxalis nasata and of the structures around it: c, heart: ep, epithelium under the cuticula (hvpodermis); or, ovarian tubes; pc, pericardial cells, with one or two nuclei containing a deposit of carmine; l and l′, group of leucocytes, which have absorbed granules of India ink.—After Kowalevsky.
Balbiani, and also Cuénot, have supposed that the formation of the blood corpuscles takes place in the pericardial cells, but Kowalevsky insists that these cells cannot form the leucocytes, which “are probably formed in different parts of the body, notably in the special nests [Herde of Jäger] situated near the heart, but outside of the pericardial cells.”
In Fig. 384, where the nests of leucocytes (l) are shown, it is evident that they are formed where observed, and “could not have come from the pericardial cells, which have their own structure and their special function,” these cells being very large and characteristic.
In Kowalevsky’s preparations of Truxalis, the pericardial cells with deposits of carmine and the groups of leucocytes (Fig. 385, l and l′) stained with India ink, we have to deal with elements absolutely different. If the formation of leucocytes was caused by the pericardial cells, these last would be obliged to free themselves from their contents and to modify their essential nature.
c. The œnocytes
Fig. 386.—Cluster of œnocytes from a nearly mature Phryganeid larva: o, œnocytes; t, large tracheal branch; tt, smaller tracheal ramifications; h, tracheal hypodermis.
