126 PHYSIOLOGY OF THE lAVERTEBRATA. 



and there are present coloured and colourless corpuscles. 

 The perivisceral fluid of the Annelida is colourless, and 

 contains colourless nucleated corpuscles. 



The corpuscles in the blood of the Invertebrata are of 

 different sizes, and the size varies much in the same in- 

 dividual. The size of the corpuscles in the earthworm and 

 leech are as follows : — 



Zdtmhricus , , . ^-fj inch in diameter. 

 Birudo .... ^swir inch in diameter. 



Their form, however, is generally spherical ; and their 

 surface has a raspberry appearanc^. 



In the higher Invertebrata the blood clots after a variable 

 period of time. 



Drs. J. B. Haycraft and B. W. Carlier* have recently 

 examined the coagulation of the blood in certain forms of the 

 Invertebrata. According to their investigations, " in Inverte- 

 brate blood the clot is formed, at any rate for the greater 

 part, by the welding together of blood-corpuscles. These 

 throw out processes, which interlace to form a solid mass." 

 Haycraft and Carlier have examined the blood of a crab and 

 a sea-urchin. 



" Crab's blood clots in about five minutes, when the opaque 

 pinkish fluid becomes water-clear, with a branching clot 

 within it. During and after coagulation the clot becomes of 

 a brown-black colour, from the development within the 

 corpuscles of a pigment." 



" The blood of the sea-urchin varies very much in the 

 number of corpuscles present in the diflerent specimens. In 

 most cases, when allowed to coagulate, the clot is very 

 small, and not easy to demonstrate in a few drops of blood." 



The blood of the higher Invertebrates generally darkens 

 rapidly on "exposure to air. For example, Mr. E. B. Poulton, 

 F.E.S.,t has shown that the blood of Lepidopterous larvffi and 



* Proc. Roy. Soc. Edinb.,vol. 15, p. 423. 

 t Proceedings of Boyal Society, 1885, p. 294. 



