136 CHANGES FROM STAGE G TO BIRTH. 



which I am inclined to agree, although I am not aware that 

 fat bodies are as a rule present in the pericardium. 



Mr. Heathcote, however, informs me that in the Myriapoda 

 a portion of the fat body does lie in the pericardium, and 

 resembles in its relation to the heart the pericardial tissue of 

 Peripatus. A tissue exactly like the pericardial tissue is 

 foundin the lateral compartment of the body cavity (PI. XT, 

 fig. 11). It has beeu noticed by Balfour and GafFron. It 

 seems to me probable that this tissue, which lies in the vascular 

 system, is of the same nature as the lymphatic tissue of the 

 Vertebrata, with which it undoubtedly presents many points of 

 resemblance. The botryoidal tissue of Leeches (Lankester) and 

 the brown cells of Chsetopoda may possibly fall into the same 

 category. The former presents very much the same relations 

 to the vascular system, but the latter diflFers by lying in the 

 coelom. 



In Stage g the horizontal septum which divided the central 

 compartment of the body cavity into a dorsal [b. b. c.') and 

 ventral {b. b. c, PI. IX, fig. 43) chamber breaks down. 



Both the pericardial and lateral compartments of the bodj'' 

 cavity (hsemocoele) seem to communicate with spaces amongst 

 the muscles of the body wall. One such set of spaces is especially 

 conspicuous between the ectoderm of the ventral body wall and 

 the circular muscles (PI. XI, figs. 11). This system of spaces, 

 which is probably segmentally arranged, communicates with 

 the spaces in the legs. It is, I think, the blood in these 

 ventral vascular channels wliich exudes through the ventral 

 organs when the animals are contracted by the action of 

 chloroform. 



The ostia of the heart appear to arise in Stage g. I have 

 no satisfactory observations of them. They are, I think, con- 

 fined to the posterior end of the heart in the Cape species. 



The main vascular tracts, therefore, are five in number, or, 

 to put it in another way, the h^emoccele is divided into five 

 main chambers : (1) the central compartment of the body 

 cavity ; (2) the heart ; (3) the pericardial cavity ; (4) the two 

 lateral compartments or lateral sinuses (in which the nerve- 



