252 



Mr. P. Geddes. On the Coalescence of [Mar. 18, 



Like haemoglobin and haematin, urobilin appears to be a very unstable 

 body, which easily splits up on treatment with reagents into decom- 

 position products, each giving a peculiar spectrum. 



III. " On the Coalescence of Amoeboid Cells into Plasmodia, and 

 on the so-called Coagulation of Invertebrate Fluids." By 

 P. Geddes. Communicated by Professor Burdon Sander- 

 son, F.R.S. Received March 13, 1880. 



[Plate 5.] 



Whether one collects the perivisceral fluid of a sea-urchin or of a 

 worm, or the blood of a crustacean or a mollusc, the same phenomenon 

 is always more or less distinctly to be observed. A kind of coagulation 

 takes place, the fluid separating sooner or later into two portions, which 

 have considerable superficial resemblance to the clot and serum of 

 vertebrate blood. 



It is easy to watch the formation of the clot by placing a drop of 

 fresh-drawn fluid upon a cover-glass and inverting this above a glass 

 cell, of which the edge is oiled to prevent evaporation. The drop 

 thus hangs freely and the coagulation can go on without interference. 



The phenomena observed in various invertebrates are best under- 

 stood by reference to the plate. Fig. 1 represents some of the groups 

 into which the amoeboid corpuscles of the perivisceral fluid of the 

 earthworm run immediately after drawing. In fig. 2 we have a few 

 adjacent corpuscles from the gill of Pholas; in fig. 3 they are com- 

 mencing to adhere ; in 4 and 5 their adhesion is complete ; in fig. 6 

 they have all but completely merged into one mass, which is about to 

 absorb a new-comer ; in figs. 8 and 9 the mass is now completely 

 homogeneous, is altering its form and throwing out pseudopodia in all 

 directions. Figs. 10 — 12 represent the similar union of corpuscles of 

 Patella, and figs. 13, 14 those of Buccinum. 



In Pagurus the corpuscles are of two very markedly different kinds, 

 the coarsely and the finely granular. The former are much elongated 

 when freshly drawn, but rapidly become oat- or egg-shaped, and then 

 throw out blunt pseudopodia from any part of their surface. These 

 stages are represented in fig. 15. The finely granular corpuscles, 

 drawn separately at fig. 16, send out filamentous pseudopodia, and 

 alone possess the power of union. Fig. 17 represents a small clot, 

 formed by the union of the finely granular corpuscles, and containing 

 a number of coarsely granular corpnscles, which do not merge into the 

 surrounding mass. The large pseudopodial process of hyaline ecto- 

 plasm on the left of the figure is worthy of notice. 



Figs. 18 — 23 show the union of five of the finely granular corpuscles 



