NOTES ON EGHINODERM MORPHOLOGY. 607 



did not illustrate it by another of his admirable figures. In 

 any case, however, he is to be credited with the discovery of 

 the blood-vascular ring in Spatangus, though not regarding 

 it in the same way as most other authors would 



In accordance with his peculiar views he described the 

 water-tube as double along the whole length of the gullet, 

 meaning that there are two canals, as stated by Teuscher. 

 One of these, that farther from the gullet, is somewat irregular 

 and sinuous in form, being lined by large cells with volumi- 

 nous granular nuclei and masses of pigment, while the more 

 uniform vessel, closer to the gullet, is lined by small epithelial 

 cells. "An point oii Toesophage se termine, le canal sinueux 

 s'amincit peu a peu et cesse d'etre distinct; il se confond avec 

 le deuxierae canal qui reste des lors unique et continue son 

 chemin jusqu'a Textr^mite de la courbure inferieure et de la 

 jusqu'a I'organe d'excr^tion." After the disappearance of this 

 sinuous pigmented canal the more uniform one remains of the 

 same character until it reaches the diverticulum. Its lumen then 

 becomes divided up by partitions, and its cellular lining con- 

 sists of larger elements with granular nuclei, so that it passes 

 gradually into the so-called excretory organ. Koehler speaks 

 of it as the water-tube^, not only communicating with the gland, 

 but in perfect structural continuity with it ; and it is doubtless 

 the one described by Teuscher as the water-tube between the 

 gland and the gullet. But I much doubt its really belonging 

 to the water-vascular system ; and it appears to me to 

 correspond to the ''glandular canal" of Echinus, which 

 likewise connects the gland with the oral, blood-vascular 

 ring. 



Towards the apical extremity of the gland, where its charac- 

 teristic parenchyma becomes less developed, two special canals 

 differentiate themselves. 1. The " madreporic canal," more 

 centrally placed, often containing coagulum, and the first to 

 appear at the tapering upper end of the gland, which it resem- 

 bles in structure. 2. A more peripheral one lined by a 

 regular columnar epithelium. The glandular tissue finally 

 ' Op. cit., pp. 92—99. 



