264 FROM FISH TO PHILOSOPHER 



113, 114, 120, 121, 122, 123, 125, 126, 129}. Physiologi- 

 cal studies are reported in 46, 47, 53, 56, 57, 87, 89, 

 101, 102, 103, 106, 107, 114, ii5a-c, 117, 118, 119, 

 124, 130, 131. Additional literature is cited by Smith 

 {62, pp. 35, 110, 112, 143, 179, 183, 520, 522} and in 

 literature appended to Chapter X. 



No observations are available on the filtration rate in 

 the eel, salmon, or stickleback, in relation to migration 

 between fresh and salt water, and relatively few ob- 

 servations are available on fresh water {53} or marine 

 {106, 107, 117} teleosts generally. The longhom sculpin 

 M. octodecimspinosus has been studied extensively by 

 R. P. Forster {115}. The large magnitude of the urine 

 flow in the fresh- water eel, carp, and goldfish {46, 53} 

 impUes a correspondingly large filtration rate. 



It is clear from the studies of Edwards {112, 113} 

 that the proximal tubule in the mammal, bird, reptile, 

 and frog is cytologically uniform throughout its length. 

 However, in the glomerular nephron of the fresh-water 

 and marine teleosts, Edwards {111, 113} has shown 

 that the proximal tubule is differentiated into two por- 

 tions (or segments). According to Grafflin {122} the 

 first portion, where present, is homologous in all fish 

 kidneys; but this first portion is lost in the aglomerular 

 kidney, only the second remaining. 



Edwards {112, 113} has also shown that in typical 

 marine teleosts, whether the nephron is glomerular or 

 aglomerular, the distal tubule is regularly absent, whereas 

 in the fresh-water teleosts the distal tubule is regularly 

 present. In this respect, the common eel {Anguilla ro- 

 strata) is a typical fresh-water form, in that it possesses 

 a distal tubule {121}, whereas the stickleback, Fundulus 

 heteroclitus, is a typical marine form, in that it lacks a 

 distal tubule {112, 122}. This difference conforms with 

 other evidence that the eel, though it invades the sea, 

 has the congenital features characteristic of a fresh-water 

 habitus, and that the stickleback, though it invades fresh 



