192 JOHN TAIT. 



Although it is not my intention to discuss in detail the basis on 

 which crustacean coagulation is separated into these three types, it 

 would be a mistake to convey the impression that a hard and fast 

 line of separation can be drawn between them. The classification is 

 arrived at by examining the blood always under the same conditions — 

 that is to say, entirely removed from, the vessels and placed either in 

 a dish or on a glass slide. These are, in fact, the conditions under 

 which observations on coagulation are generally made. The classifica- 

 tion here given represents a more extended knowledge than that 

 hitherto in vogue — originally due to Heim (92) — wliich recognizes two 

 groups, viz. A and B above. 



COAGULATION C. 



It will be convenient to begin with coagulation C, which is 

 associated with the presence of explosive cells, and which from its 

 complexity must be regarded as a somewhat specialized form of 

 coagulation. 



This form seems to be specially frequent in Isopoda. I have found it in 

 Conilera cj/lindracea, in Idotea haltiea and emarginata, in Ligia oreanica, 

 in Oniscus, and in one or more species of Porcellio, i.e. in individual 

 members of three sub-orders out of six.* On the other hand, I have 

 failed to find it in Gnathia mcixillaris, in Dynamene rubra, in Spliaeroma 

 serratum,-f and in Jaera marina, though possibly owing to the fact 

 that the amount of blood obtained from these relatively small specimens 

 was too meagre to allow of a satisfactory examination. 



Among Amphipoda the occurrence of coagulation seems to be 

 much less frequent. It is not present in Gammarus marinus, in 

 Gammarits pulex, in Orehestia littorea, nor in certain specimens of 

 Caprella examined by me. On the other hand, I have recorded its 

 presence in Gammarus locusta — Tait (10, B). This was not, however, 

 under the conditions above specified — that is to say, in blood wholly 

 removed from the animal and examined separately on glass, nor have 

 I as yet observed it under these conditions. 



As regards the Mysidacea coagulation C is absent in at least one 

 species of Mysis (the only member of this order examined by me). 



Crustacean blood coagulation has been chiefly studied in the 



* The zoological classification referred to in the present paper is that given by Calniau 

 in Part VII of Lankester's Treatise on Zoology. 



t In the course of this work I found that Spliaeroma serralum (with black clnoniato- 

 phores) undergoes colour change in response to its background, like that undergone by 

 Idotea — V. Bauer (05) — and by Ligia — Tait (10, C)— whereas Oniscus and ConiJera, the latter 

 possessed of orange and lemon-yellow cluoniatophores, do not. 



