409 



hypochord in the region of the auditory vesicles have compared it with 

 the putative "head part" of Balfour. 



Salensky (42) determined the hypoblastic origin of the "ligne 

 souscordale" in Acipenser, and asserted that it become the ligamentum 

 longitudinale ventrale. 



Sutton (46) stated that the hypochord became permanent fibrous 

 tissue in Rana temporaria. 



Perenyi (33 and 34), in Torpedo, claimed that the hypochord had 

 a mesodermal origin, looked upon it as a degenerate blood vessel, and 

 believed that it took part in the formation of the skeletogenous sheath 

 of the notochord. 



Hennbguy (16) observed the hypoblastic origin and iiltimate atrophy 

 of the "tige sousnotocordale" in the salmon and trout. 



RüCKERT (40) thought at first that the hypochord in embryos of 

 Pristiurus and Torpedo supplied cells to the rudiment of the aorta, but 

 he finally decided to the contrary. A "head part" was found in the 

 former but not in the latter. 



Rabl (38) remarked that it began in the anterior trunk region of 

 Pristiurus as a series of metamerically-arranged thickenings of the 

 dorsal wall of the hypoblast. It became a continuous ridge in this region, 

 though higher opposite to the myotomes, while it had begun behind 

 also as a series of thickenings. We may safely presume that these 

 inequalities in height are due to mechanical causes. A separate "head 

 part" lay at the level of the auditory vesicles. 



Wilson (49) found in Serranus atrarius that cells flattened dorso- 

 ventrally formed a ridge upon the hypoblast in the trunk region and 

 became isolated as the hypochord. In the post-anal region the develop- 

 ment took a different course: the gut atrophied and a rod of cells 

 remained. 



V. KuPFFER (24) referred to the development of the hypochord 

 in Petromyzon Planeri only by the way, but the reference is important 

 in view of my observations. Those cells which composed the median 

 dorsal wall of the gut after the isolation of the notochord passed up- 

 wards after it to form the hypochord, the neighbouring hypoblast cells 

 closing in to complete the gut wall. 



GoETTE (11) recorded merely the atrophy of the hypochord in 

 Petromyzon fluviatilis, and not its mode of development, but his figures 

 are confirmatory of v. Kupffer's statements. 



Hasse (13) noted that in Triton taeniatus the inner layers of the 

 skeletogenous tissue around the notochord arose from a mass of cells 

 lying below the latter; but that the hypochord played a part in the 

 formation of this tissue he was unable definitely to assert. That it 

 also contributed cells to the connective-tissue sheath of the aorta was 

 suggested. Hasse showed in his figures a structureless membrane which 

 enclosed the mass of hypochordal cells; but it cannot be ranked as a 

 cuticle inasmuch as it does not closely enwrap the cells. 



Hatta (15) was able to amplify v. Kupffer's statements in the 

 case of Petromyzon. The references of v. Kupffer and Hatta have 

 escaped the notice of other workers, and became known to me only 



