FISHERY BULLETIN: VOL, 69, NO. 3 



of blood fluids into tissues, adherence of hemo- 

 cytes to blood vessel walls, and migration of 

 hemocytes into tissues around areas of injury 

 or parasitic invasion. 



The involvement of hemocytes in coagulation 

 or clot formation is a complex one, inasmuch as 

 either cellular or extracellular clots may be 

 formed. Intravascular cellular clots adhere to 

 walls of blood vessels and spaces, producing 

 stasis, and once they are formed, persist for 

 some time. Extracellular clots, resulting from 

 release of constituents of hemocytes, can inhibit 

 microbial motion and thus render microorgan- 

 isms more vulnerable to phagocytosis. Since 

 Fredricq (1879) first pointed out that in Crus- 

 tacea coagulation of hemol\Tnph involves cell 

 agglutination as well as plasma coagulation, 

 others have demonstrated similar characteristics 

 in a number of invertebrate groups. The release 

 of a component from hemocytes and the role of 

 this component in initiating coagulation of plas- 

 ma were reported by a number of authors be- 

 ginning with Halliburton (1885). Lowit (1889) 

 observed the rapid disruption of hemocytes and 

 the rapid clotting characteristic of most Crus- 

 tacea and concluded that a causal relation ex- 

 isted. Hardy (1892), Tait and Gunn (1918), 

 Tyler and Scheer (1945), and George and Nich- 

 ols (1948) all provided data which supported 

 the conclusion that a component from certain 

 hemocytes acts with fibrinogen of plasma to form 

 fibrin clots. 



Bang (1967c, 1968) demon.strated that in the 

 hermit crab, Eupaynriis lovgicarpus. clots 

 formed in at least two stages following injui'y — 

 first a clumping and stickiness of hemocytes 

 without change in shape or loss of granulation, 

 then retraction of the clot and the development 

 of a network of fibrous cell projections contain- 

 ing microtubules. 



The abundant and elaborate literature on he- 

 molymph coagulation in Crustacea was admir- 

 ably summarized and evaluated by Florkin 

 (1960) . As he pointed out, coagulation has been 

 considered by some authors to occur in two dis- 

 tinct phases— cellular coagulation and then jilas- 

 ma gelation— while other workers view coagula- 

 tion as a continuous ])rocess in which i)lasma gel- 

 ation begins around hemocvtes. It was Florkin's 



conclusion that plasmatic coagulation was a one- 

 step process in which fibrinogen of the plasma 

 was acted upon by a coagulin released by the he- 

 moc\'tes. It seems equally possible, however, that 

 more than one type of coagulable protein exists 

 and that the categories of clots may be complex 

 rather than simple. Florkin also reviewed the 

 role of cellular clots in wound repair, emphasiz- 

 ing the im]5ortance of secretion of a chitin film 

 over the wound area by underlying coagulated 

 phagocytes. 



Encapsulation is also a common form of cellu- 

 lar internal protection in invertebrates. Invading 

 organisms, often relatively large, are surrounded 

 by phagocytes and fibrocytes. The onset of 

 encapsulation may be rapid, and the cellular 

 aggregates may be resolved only very slowly. 



In summary, the hemocytes function in a num- 

 ber of ways beyond phagocytosis, although the 

 latter must be considered the dominant cellular 

 defense mechanism: 



1. Hemocytes are important in cellular infil- 

 tration of injured or diseased tissue. 



2. They are important in clotting — either as 

 participants in cellular clots, or by release of se- 

 cretions or injury products which combine with 

 plasma components to form extracellular clots. 



.3. The hemocytes are of primarj' importance 

 to encapsulation. 



A great variety of crustacean hemocytes have 

 been described during the past several decades. 

 Animals studied included crayfishes (George and 

 Nichols, 1948; Toney, 1958; Wood and Visentin, 

 1967), blue crabs (George and Nichols, 1948; 

 Toney, 1958), lobsters (Toney, 1958; Hearing 

 and Vernick, 1967) , and brine shrimp (Lochhead 

 and Lochhead, 1941). Except for size differ- 

 ences, the principal distinction seemed to be pres- 

 ence or absence of granules in the cytoplasm. 

 The hyaline hemocytes are usually smaller than 

 the granular, and some of the hyaline cells 

 probably develop into the granular types, since 

 the intergrades have been noted (Cuenot, 1895). 

 As was aptly pointed out by Rabin (per-sonal 

 communication), "The developmental relation- 

 ships of one form of hemocyte to another which 

 have been made amount to little more than edu- 



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