and Anatomy of the Echinodermata., 373 



Thus in the Spatangida there has occurred a fusion of the 

 cavitarj systems, which in the Asterida are separate. In the 

 dorsal part the blood-lacunee run in the wall of the schizocoele- 

 sinus, as I have shown for the first time. In this, therefore, 

 these forms agree with the regular Echinida and the 

 Asterida. 



Let us now consider the Holothuriae. In Synapta there is 

 a blood-lacunar ring of very feeble construction running in 

 the wall of the annular water-vascular canal. From this 

 blood-lacunge issue to the tentacular canals. In this genus no 

 schizocoele-cavity runs through the five ambulacra. In the 

 foot-bearing Holothurise, which show more primitive con- 

 ditions, however, we again find the five radial ambulacral 

 schizocoele-cavities J here thej may justly be denominated 

 blood- lacunse. 



In the Crinoidea we find radial longitudinal canals, which, 

 as I propose to demonstrate immediately, are likewise schizo- 

 coele-structures, and are, certainly with justice, described as 

 the radial blood-vessels by Ludwig. GreefF and Ludvvig 

 declared them to be homologous with the radial longitudinal 

 canals (perihsemal cavities of Ludwig) in the Asterida. Sub- 

 sequently Ludwig has retracted this opinion, because he 

 thinks that the longitudinal canals of the Asterida are not 

 themselves blood-lacunse, but that the latter are situated in 

 the septa, so that the blood-lacunse of the Asterida and Cri- 

 noidea are quite different structures. The foundation of this 

 opinion is to be found in the fact that Ludwig regarded the 

 longitudinal canals as enterocoele-structures. When Ludwig 

 further says that in the Crinoidea no perihsemal cavities have 

 yet come into development, either in the periphery of the oral 

 blood- vascular ring or in that of the radial blood-vessels, we 

 may reply as follows : — The radial blood-vessels (so-called) of 

 the Crinoidea and their oral blood-vascular ring are nothing 

 but the radial longitudinal canals (perihasmal cavities) of the 

 Asterida and their oral annular canal. Bat while in the 

 Asterida special lacunae, the true blood-lacunse, have been 

 developed in septa, the septa are wanting in the Crinoidea, 

 The blood moves in the longitudinal canals, as is partially the 

 case in Spatangida and Holothuri^. 



Further, the Crinoidea also possess other radial schizocoele- 

 canals (homologous with the dorsal cavities of the other 

 Echinodermata), and in these (in septa) blood-lacunse occur, as 

 will hereafter be shown in detail. 



Summing up briefly all these conditions, it appears that no 

 decided difference exists between true blood-lacuna3, situated 



