580 RECORD OP CURRENT RESEARCHES RELATING TO 



vascular system of the Asterida ; this consists of the following 

 parts : — 



1. An oral blood- vascular ring placed in the peristom. 



2. A dorsal blood-vascular ring. 



3. A vascular plexus connecting these rings — the so-called heart. 



4. A radial vessel given off from (1) to each arm. 



5. Vessels given off from the dorsal vascular ring, and passing to 

 the generative organs. 



6. Two gastric vessels given off from the dorsal vascular ring. 



To turn to what obtains in Brisinga, and following the author in 

 first discussing the genital vessels, which are the easiest to find, wo 

 discover a vessel to the right and to the left of the series of joints of 

 which an arm is made up ; as it reaches the genital organs this vessel 

 nearly doubles in breadth ; examined in cross section, it is seen to 

 contain a plexus of vessels, so that it is a " peri-htemal canal " ; the 

 plexus has just the same characters as in the rest of the Asterida, 

 save only that it is more distinctly plexiform ; in its terminal cha- 

 racters it exactly resembles the genital vessels of the true sea-stars. 

 The radial blood-vessels were examined by the aid of sections made 

 through decalcified arms, and were found to be in all essential cha- 

 racters exactly similar to the same parts in the Asterida ; the same is 

 the case with the vascular apparatus of the disk ; therefore we are 

 relieved from describing it here. 



On the dorsal aspect of the disk Sars observed a pore, which was 

 subcentral in position, but which he only regarded as the orifice of an 

 excretory aj^paratus, as he was unable to discover any connection 

 between it and the enteric tract. Ludwig now shows that this pore 

 communicates with the lumen of the interradial ctecal sacs, which are 

 given off from the stomach, and which are shown by further examination 

 to be nothing else than processes of the rectum, so that the pore is a 

 veritable anus. In another point, also, Ludwig extends the observa- 

 tions of Sars, to make which clear it is necessaiy to draw attention to 

 the fact that our author, in his examination of the peristomial skeleton 

 of the Asterida, has discovered that the first two joints of the arms 

 undergo more or less complete union. Now, according to Sars, this 

 region consists of two joints, with their adambulacral plates, for each 

 radius, and two j)aired " dorsal marginal plates " for each interradius ; 

 while there are, in addition, in, each interradius, two " parietal " plates ; 

 these last are now shown to be the first and metamorphosed joints, and, 

 just as in the rest of the Asterida, the so-called first joint is really 

 double, for Sars erred in regarding them as interradial instead of radial. 



A few words must be said as to that peculiarly interesting struc- 

 ture—the stone canal. A series of transverse sections has demon- 

 strated that, as in all other Asterida which have as yet been examined, 

 it commences by a simple lumen ; just as in Echhiaster fallax, its 

 structure is not at all complicated, as it is, for example, in Asterina 

 •pentagona ; its investing epithelium is high and ciliated, and the cuticle 

 is traversed by small but quite distinct pore-canals for the passage of 

 the cilia, and each j)orc-canal seems to belong to a i)ropcr epithelial cell. 



As may now be supposed, Ludwig inclines to the view of Sars 



