The development of the urinogenital organs of the lamprey. ß5 



knowledge of the glomus and glomerulus, albeit along different 

 lines. 



Felix (1897 a and 1897 b) has shown that the pronephric chamber 

 of Salmonids and probably also of Ganoids, does not arise as Goette 

 would have us believe as an abstricted portion of the body cavity 

 proper, but as a dilatation in the pronephric tubule. Into this cavity 

 the glomerulus is protruded. Hence the pronephric chamber of fishes 

 is not the homologue of the Amphibian pronephric chamber. He 

 concludes, therefore, that we must distinguish two very different types 

 of pronephric chamber, one formed by the blind dilated termination 

 of the pronephric tubule (with inner glomerulus), the other by a more 

 or less complete abstriction of a portion of the true body cavity (with 

 outer glomerulus, or glomus). To the former category belong the 

 pronephric chambers of Teleostei, Ganoidei and probably IcMhyophis, 

 the very form which led Semon to his generalizations, but of which 

 he did not see the early developmental stages ^). These considerations, 

 as Felix demonstrates at some length, show that Semon's search up 

 and down the Vertebrate phylum, for "inner and outer funnels" is 

 utterly futile. In fact, the absence of "outer funnels" in Urodela 

 shows that even the Amphibia will not fall within the general schema 

 which he has so zealously attempted to establish. 



To the two forms of the glomerulus recognized by Felix, a third 

 may be added, viz. that which occurs in Petromyzon. Here the glomus 

 hangs freely into the body cavity (pericardial coelom) instead of pro- 

 jecting into a more or less completely abstricted portion of the body 

 cavity or into the dilated lumen of the distal end of the pronephric 

 tubule. This simple condition in Petromyzon would seem to represent 

 the most primitive of the three conditions. From it to the Amphibian 

 condition the passage is easy and direct. The gap between the Am- 

 phibian and Teleost pronephric chamber is of a different character 

 and both have probably arisen under very different phylogenetic con- 

 ditions. 



Both inner and outer glomeruli may change their form by fusion. 

 In the former case the cavities in the closed tips of the pro- 

 nephric tubules may become confluent and their enclosed glomeruh may 

 unite to form a single compound glomerulus. Similarly, but with greater 

 readiness, the metameric glomi may unite to form a single glomus. 



1) Similar criticism may be applied to Wiedbrsheim's work on the 

 crocodile and seaturtle. 



Zool. Jahrb. ÏIII. Abth. f. Morph. 5 



