ABSTRACT
Howell (1885) observed that the blood of Limulus polyphemus, the horseshoe crab, formed a solid clot when withdrawn from the crab. Loeb (1902) noted that when the blood cells of Limulus were collected and exposed to foreign substances, they coagulated. These were the first papers detailing various aspects of coagulation with reference to amebocytes, which are the only circulating cells found in the blood of Limulus.
