SKELETO-TROPHTC TISSUES AND COXAL GLANDS. 143 



cells and when seen in thickish sections has the appearance 

 shown in PL XI, fig. 8. 



The lacuna or central space of each capsule (always commu- 

 nicating by a gap in its wall with the lacuna of one or more 

 neighbouring capsules) contains an albuminous liquid, which 

 sometimes is seen in the form of a coagulum in sections of the 

 tissue hardened in spirit. According to varying conditions 

 (probably the state of nutrition of the animal) the lacunae will 

 be large, and the protoplasm of the cells lining the capsule 

 sparse and thin, spreading as a film over the surface of the 

 capsule, or on the other hand, the lacuna will be much 

 reduced, possibly obliterated by the rich development of the 

 protoplasm of the lining cells, which then stand out as large 

 masses, pressing against one another and filling up the lumen 

 of the capsule. These two states of the lacunar tissue are 

 probably also permanently exhibited in varieties of the 

 tissue from different parts of the body. 



The exceedingly important question now arises — ' What is 

 the nature of the lacunae and their contained fluid ? ' At 

 first sight one is disposed to take the view that these 

 lacunae are part of the general " lacunar blood system " 

 universally ascribed to the Arthropoda, and very possibly they 

 are so. But at present I have no evidence to show that they 

 are. I have never found blood- corpuscles floating in these 

 lacunae, nor have I seen any blood-vessel enter into open com- 

 munication with them. At present, also, I have not succeeded 

 in injecting them with soluble Berlin blue when such injection 

 is made either by way of the arteries from the iieart, or by 

 way of the great veinous sinuses by use of a puncturing 

 syringe. The further investigation of the relation of this 

 tissue to the vascular system will occupy some time and can 

 be most appropriately discussed in connection with an exami- 

 nation of the circulatory and respiratory organs with which I 

 am occupied. 



The lacunar connective tissue of both Limulus and Scorpio, 

 unlike the fibro-massive skeletal tissue, is vascular. Not unfre- 

 quently one observes in a section of this tissue fine blood- 



