Blood Coagulation in Arthropods : II. Phase Contrast Microscopic Observations on Hemolymph Coagulation in Sixty-one Species of Insects

1. Thin films of freshly drawn hemolymph of about 360 insects belonging to 61 different species were observed under the phase contrast microscope and the process of coagulation investigated. Control of the observations by motion picture recordings were performed in a few species.

2. In the hemolymph of all the insects investigated, a category of hyaline hemocytes can easily be recognized under the phase contrast microscope from the other kinds of blood cells. Attempts of identification of these hyaline hemocytes with elements described in the classifications of insect blood cells based on fixation and staining were inconclusive.

3. In the insects in which the blood clotting does not occur, these hyaline hemocytes do not exhibit any important alteration. In species inn which blood coagulation occurs, the cells of this category appear to be highly labile to contact to glass surfaces. They undergo rapid modifications in their structure which play an important if not exclusive part in the initiation of the plasma coagulation. In the present material these alterations are of two kinds, each of them being related to a different appearance of the plasma reaction. They can occur alone or together.

4. In contrast to the hyaline hemocytes, the other categories of blood cells do not take part in the process of coagulation. Scattered or agglutinated at random, they are passively embedded in the coagulum.

5. In the present material, hemolymph coagulation appears to be a continuous process, initiated by alterations taking place in a single category of hemocytes. These alterations are followed by various degrees of plasma coagulation, from a general macroscopic clotting to a limited reaction detectable only under the microscope.

6. The results are at variance with former data in which the coagulation of insect blood was described as being either a cellular agglutination, in which no special part was recognized to be played by a special category of cells, or a plasma coagulation, both considered as two physiologically distinct processes, which can occur independently or together. On the other hand, the present results show an analogy with the type of coagulation described in crustacean blood by Hardy, Tait, Tait and Gunn, in which a special category of cells, Hardy's explosive cells, as distinguished from the other blood cells, has a specific and important part to play.