The development of the uriiiogenital organs of the lamprey. 5 



welche in einen schmalen, längs der Chorda eine Strecke weit nach 

 rückwärts verfolgbaren Gang führte". In an older embryo (4,25 mm 

 long) with the definitive numlier of gill-sacs, there were two of 

 these tubular projections opening into the body-cavity above the heart. 

 The projections were found to communicate with coiled tubules that 

 could be traced between the chorda and peritoneum from the hinder- 

 most gill-septum to the level of the anterior surface of the liver. All 

 of these structures had a distinct lumen and consisted of a single 

 layer of cuboidal cells and a thin layer of connective tissue. The 

 coiled tubules were connected on either side with a duct, which ran 

 along the ventral surface of the chorda to within a short distance from 

 the cloacal orifice. 



In an Ammocœtes 7 mm long Wilhelm Müller found four pro- 

 trusions and describes these as each opening with a "trichterförmig 

 von zwei Seiten compriniirte Oeffnung in die Peritonealhöhle". He 

 observed the cilia in these openings and other details in the histo- 

 logical structure of the tubules. On the mesial side of each pro- 

 nephros Mt)LLER saw the glomus covered with peritoneal epithelium. 

 The coiled pronephric tubules were traced to their union with the 

 duct and this was followed back along the lateral and ventral sur- 

 face of the "Vena cava" (Vena cardinalis posterior) to its opening 

 into the cloaca. In larvae of P. planeri 25 mm and 43 mm long the 

 number of funnels was found to be the same and apart from an in- 

 crease in size there was little change in the pronephros. In the latter 

 stage the organ is described as "von ziemlich weiten Gefässräumen 

 durchsetzt". In a larva 6,5 cm long the organ is said to be "in 

 voller Rückbildung begriffen". This process was accompanied by the 

 appearance of great cavities communicating with the cardinal vein. 

 These cavities cause the pronephric tubules to spreail apart. The cells 

 of the tubules are filled with "braunen kryptokrystallinischen Körnchen". 

 In the adult Tetromyson during the spawning period "hat die Vorniere 

 eine nahezu complete Involution erfahren". Only the funnels and the 

 glomus are unaffected by this change, the former still retaining their 

 cilia and compressed shape, the latter remaining attached to the peri- 

 toneum by means of a narrow peduncle. The tubules, however, have 

 disappeared together with the anterior end of the pronephric duct. 



FÜRBRINGER (1878) Studied Calberla's sections of Petromyzon 

 planeri (embryos and Ammocœtes 4,5 — 180 mm long). The pro- 

 nephros was already formed in the youngest stage examined. Both 

 Calberla and Fürbringer found five funnels, and the glomus as 



