CRUSTACEAN BLOOD COAGULATION. 195 



two otlier conditions with which at one time I imagined coagulation C 

 might possibly be correlated. Having discovered coagulation in 

 isopods long before I found it in any decapod, I looked for other 

 physiological peculiarities characteristic of isopods as opposed to 

 decapods. An obvious one is the peculiar method of moulting observ- 

 able in isopods. A moulting isopod throws oft" first the covering of the 

 abdomen along with that of the posterior three thoracic segments. At 

 a later date the covering of the head and anterior four thoracic 

 segments is got rid of.* In decapods the moulting process does 

 not occur in two stages. Once again, a fact to which attention 

 has not been called, so far as I know, isopods do not turn red on 

 boiling as so many decapods do. The discovery, however, of coagula- 

 tion C in decapods, which moult in a difterent fashion and turn red on 

 boiling, disposed of any possibility of establishing a correlation with 

 these two phenomena. 



COAGULATIONS A AND B. 



Before discussing coagulation C in its zoological bearing, it may be 

 well to make some statements regarding the distribution of the other 

 two forms of coagulation, viz. types A and B. To determine the 

 existence of one or other of these two types a greater quantity of 

 blood is necessary than when one looks merely for the presence of 

 coagulation C. Partly for this reason my data are somewhat meagre, 

 and refer only to fairly large Crustacea of the order Decapoda. The 

 results agree to some extent with those of Heim (92). 



Coagulation A is present in Cancer pagurus, Maia squiiiado, Inachns 

 dorifiidins, Macropodia rostratns, and Hz/as coarctatns. 



Coagulation B is present in Carcinus macnas, Pcdaemon scrratus, 

 Portiums 2Juber, and Homarus vulgaris. 



The last four animals are arranged in order according to the extent 

 and firmness of the plasma jelly that forms in their blood after with- 

 drawal. In Carcinus maenas the bulk of the plasma remains indefinitely 

 fluid ; in Palaemon the jelly, which is soft, involves almost all the 

 plasma ; in Portunus tliere is a complete and fairly firm jelly ; while 

 the plasma of Homarus clots with exceptional firmness. 



I should like to make two comments on these results. In the first 

 place, there is a complete series of gradation of plasma coagulation 

 to be observed in group B. The amount of plasma jelly formed 

 in the blood of Carcinv.s macnas is so slight that we might almost 



* I do not know that anyone lias called attention to the fact that tiic separation 

 between the two cast-ofl' jiortions of the integument occurs just at the anterior limit of the 

 heart, as determined by the researches of Delage (81). 



