408 



GoETTE (9 and 10) determined the origin of the "Achsenstrang des 

 Darmblattes" in Bombinator from the hypoblast. Appearing first as a 

 ridge upon the latter, and eventually separating, it took up a position 

 below and against the notochord, the aorta forming between it and the 

 gut. Fully developed, it reached from the middle of the fore-gut to the 

 end of the tail-gut. Observing processes hanging below which projected,^ 

 as he then believed, into the lumen of the aorta, he looked upon them 

 as blood-forming organs. But this suggestion about their function was 

 later withdrawn; when, with some doubt in his mind, he then thought 

 that from the hypochord was derived part of the lymphatic system. 



Oellacher (32), though he observed its derivation from the hypo- 

 blast in the trout, applied to it the term "Aortenstrang", for he saw in 

 it the rudiment of the aorta. 



Semper (43), in his Selachian material, noted the ultimate dis- 

 appearance of the "hypochordalen oder subchordalen Zellenstrang". His 

 prophecy was that it would play a part in the working-out of the verte- 

 brate phylogeny through the invertebrates. 



Eisig (5), having drawn attention to the "Nebendarm" of the 

 Capitellidae, to the intestinal siphon of Echinoids, and to a somewhat 

 similar organ in Bonellia, speculated as follows: "Durch die Zuriick- 

 führung des hypochordalen Stranges gewisser Teleostier, Selachier und 

 Amphibien auf den Nebendarm der Capitelliden ist eine neue Brücke 

 zwischen Anneliden und Vertebraten geschlagen, und durch den Nach- 

 weis des Vorkommens eines Nebendarraes bei Vertretern der Anneliden, 

 Gephyreen und Echinodermen ist auch ein neues Bindeglied zwischen 

 diesen, ohnedies schon so vielfach verwandten, Gruppen hergestellt". 

 Later, in the monograph (6), his front was changed; the notochord was 

 homologised with the "Nebendarm", and the hypochord with the ciliated 

 groove of Echinoids. In the supplement to this monograph, after point- 

 ing out that KoEHLERS (23) had discovered a second intestinal siphon 

 n Schizaster, Brissus and Brissopsis, he proceeded : "Wir können fortan 

 ^owohl die Chorda, als auch den subchordalen Strang auf successive zur 

 Abschnürung gelangte Nebendärme beziehen," 



Balfour (2 and 3), in Elasmobranchs, saw the trunk part develop© 

 first: "The wall of the alimentary canal becomes thickened along the 

 median dorsal line or else produced into a ridge into which there 

 penetrates a narrow prolongation of the lumen of the alimentary canal. "^ 

 In the tail a part of the wall of the alimentary canal was scooped out 

 to form the hypochord. In the head it arose in the same manner as 

 in the trunk. It extended from a point short of the anterior end of 

 the notochord to a point short of the neurenteric canal. Its dis- 

 appearance was complete. Balfour used the following words, which 

 have been interpreted as meaning that the hypochord is a bipartite 

 structure: "We may distinguish two sections of it, the one situated in 

 the head, the other in the trunk. The junction between the two occurs 

 at the hind border of the visceral clefts." Why this distinction was 

 made is not evident, for nowhere is it shown that the two sections 

 differed in character or in mode of development or arose separately. 

 Unfortunately, some workers who have found a separate part of the 



