NOTES ON EOHINODERM MORPHOLOGY. 609 



regards the gland, and also that it is not continuous, indepen- 

 dently of the " glandular canal " with either of the two canals 

 arising from the peribuccal rings. I will assume, though Koehler 

 nowhere says so, that the more sinuous pigmented canal which 

 " disappears " higher up, starts from the water-vascular ring ; 

 while the other, which eventually becomes glandular, is con- 

 nected with the blood-vascular ring as in Echinus. If this 

 be the case, it would seem that the Spatangids, like the 

 Crinoids, and possibly also the Ophiurids, have an interrupted 

 water- tube arising from the water-vascular ring; though in- 

 direct communication between the two is effected by the body- 

 cavity into which both tubes open by their inner ends. This 

 seems to me much more probable and in better accordance with 

 the morphology of Echinoderms generally than the position 

 taken up by Koehler. According to him the " madreporic 

 canal" of Spatangus is to be considered as the water-tube, 

 though it lacks the characteristic columnar epithelium. It is 

 further comparable in every respect, as Koehler himself admits, 

 to the so-called excretory duct of the ovoid gland in Echinus, 

 and therefore, also in other regular Echinoderms. In both Aste- 

 rids and Ophiurids this " excretory duct " is said by Ludwig to 

 join an aboral ring in which the genital vessels arise; and 

 certain points in Koehler's memoir lead me to think that the 

 same may be the case in the Urchins. Various facts mentioned 

 by Hoffmann, Perrier, Teuscher, and Koehler, more especially 

 by the two latter, who are the only ones to figure sections of 

 the ambulacra, also indicate that the system of perihaemal 

 spaces originally derived from the coelom, which have been 

 described under various names in the Asterids and Opliiurids, 

 really occur in the Urchins too. But on this point, as on many 

 others, Ave shall doubtless be enlightened by Ludwig himself. 



I have already alluded to the recently published note by 

 Professor Perrier, " On the organisation of Crinoids." He, 

 of course, uses the somewhat inappropriate term " ovoid 

 gland " in speaking of the central plexus, but says nothing 

 whatever about its having any communication with the exterior. 

 This is not very surprising, for the water-pores of a Crinoid 



