144 PROFESSOE E. RAY LANKESTER. 



vessels lying in the capsular wall of contiguous lacunae. Such 

 fine vessels are seen in PI. XI, figs. 2 and 3 bv. 



These vessels contain when thus observed in sections, a 

 blood clot and blood corpuscles. Their proper walls appear 

 to be formed by a single layer of cells. 1 have not obtained 

 any evidence as to the termination of these vessels. On 

 the one hand it is possible that they terminate in cords of cells 

 set in single file which become excavated so as to form true 

 capillaries; on the other hand they may open into the lacunas. 

 The latter is by far the more likely mode of termination, but 

 at present I have not succeeded in observing it. 



Besides blood-vessels we find in Limulus other fine spaces 

 excavated in the capsular walls of the lacunar tissue. These are 

 the genital ducts and testicular ampullse of the male. The female 

 genital canals of Limulus and both the male and female glands 

 of Scorpio are of larger size so that they are simply packed 

 by the lacunar tissue just as the gastric coeca are. But the 

 coeca and finest canals of the male apparatus of Limulus are 

 so small and so much ramified as to become very intimately 

 interwoven with the lacunar tissue (see PI. X, figs. 1 and 2 o). 



Pigmentiferous tissue is largely developed in Limulus, 

 and io a less extent in Scorpio, by the simple accumulation of 

 pigment granules in the protoplasm of cells lining or filling the 

 capsules of lacunar tissue. The whole of the lacunar tissue 

 immediately underlying the prosomatic carapace is pigmented 

 in this way (see this Journal, vol. xxiii, plate xii, fig. 34). 

 The pigmentiferous property is by no means confined in either 

 Limulus or Scorpio to connective tissue of the lacunar type. 

 Networks of penetrating branched cells, containing pigment 

 granules, occur in some parts, the " capsule " and " lacuna " 

 having disappeared. 



4. Reticular connective tissue or Limulus. 



It is easy to understand how — by a reduction in the skeletal 



substance forming the incomplete capsules of lacunar tissue, so 



that it became a series of fine branched and reticulate cords, 



with here and there a cell resting on them — we could pass from 



