150 PROFESSOR E. RAY LANKESTER. 



toplasm less active in enclosing themselves (as soon as they are 

 formed by fission) in a new complete investment of capsule sub- 

 stance, so that several cell units were disposed around the 

 concave wall of a capsule, we should have the condition which 

 characterises the lacunar tissue. 



The difference lies merely in this, that capsule-formation 

 proceeds less energetically in the lacunar than in the capsuli- 

 genous tissue; in the former the skeletal capsule-forming pro- 

 duct is only produced in such a way as to enclose several cells ; 

 in the latter every cell completes or nearly completes a capsule 

 for itself. The space or lacuna in the centre of each group of 

 cells enclosed by the trabeculaj of the lacunar tissue (see 

 PI. X, fig. 1 e) is the same thing as the space unoccupied by 

 protoplasm within the capsule of the capsuligenous tissue, and 

 in both cases the space of one capsular area is in communi- 

 cation with neighbouring similar spaces, so as to form a 

 spongy or reticular lacunar system. 



Whether this system is (as seems probable) in communication 

 with the blood-vessels and large blood-lacunae I am unable to 

 decide in reference to the capsuligenous tissue, equally as in 

 reference to the lacunar tissue. 



Like the lacunar tissue, the capsuligenous appears to be 

 penetrated by small blood-vessels, which lie between the cap- 

 sules (PI. XI, fig. 4 x). That these structures {x) are blood- 

 vessels is, however, doubtful. 



It is stated by G-egenbaur that this capsuligenous tissue is 

 found also in the hollow gill-laminse of Limulus, forming the 

 substance of the numerous " pillars " which unite the two 

 membranes of which each lamella consists. I have not suc- 

 ceeded in finding this tissue in that position. 



I have not made a special chemical examination of the 

 capsuligenous tissue. 



8. The blood-corpuscles of Limulus and Scorpio. 

 There is a very striking agreement between Limulus and 

 Scorpio in the form, size, and granulation of their blood- 

 corpuscles, as also in the appearance of the blood when shed. 



