584 AMPHIBIA. 



limb the blind end of which assists in forming a Malpighian body, and a 

 lateral limb which comes in contact with and opens into the segmental 

 duct, and an intermediate portion connecting the two. At the junction 

 of the median with the intermediate portion, and therefore at the neck of 

 the Malpighian body, a canal grows out in a ventral direction, which meets 

 the peritoneal epithelium, and then develops a funnel-shaped opening into 

 the body cavity, which subsequently becomes ciliated. In this way the 

 peritoneal funnels which are piesent in the adult are established. 



The median and. lateral sections of the segmental tubes become highly 

 convoluted, and the separate tubes soon come into such close proximity 

 that their primitive distinctness is lost. 



The first fully developed segmental tube is formed in Salamandra 

 macuhita in about the sixth myotome behind the pronephros. But in the 

 region between the two structures rudimentary segmental tubes are de- 

 veloped. 



The number of primary segmental tubes in the separate myotomes of 

 Salamandra is as follows : 

 In the 6th myotome (i.e. the first with a true 



begraei)tal tube) . . , . . 1 — 2 segmental tubes 



„ ,, 7th — 10th myotome .... 2 — 3 ,, ,, 



,, ,, llth ,,...,, o 4 ,, „ 



„ , l^th „ 3— 4 or 4— 5 „ 



„ ,, i3th „ 4—5 „ „ 



„ „ 13th— 16th „ 6—Q „ „ 



It thus appears that the segmental tubes are not only more numerous 

 than the myotomes, but that the number in each myotome increases from 

 befoi'e backwards. In the case of Salamandra there are formed in the 

 region of the posterior (10 — 16) myotomes secondary, tertiary, etc. segmental 

 tubes out of independent solid cords, which arise in the mesoblast dorsally 

 to the tubes already established. 



The secondary segmental tubes appear to develop out of these cords 

 exactly in the same way as the primary ones, except that they do not join 

 the segmental duct directly, but unite with the primary segmental tubes 

 shortly before the junction of the latter with the segmental duct. In this 

 way compound segmental tubes are established with a common collecting 

 tube, but with numerous Malpighian bodies and ciliated peritoneal 0})en- 

 ings. The difference in the mode of origin of these compound tubes and 

 of those in Elasmobranchii is very striking. 



The later stages in the development of the segmental tubes have not 

 been studied in the other Amphibian types. 



Ill Coeciliidaj the earliest stages are not known, but the tubes pre- 

 sent in the adult (Spengel) a truly segmental arrangement, and in the 

 young each of them is single, and provided with only a single peritoneal 

 funnel. In the adult however many of the segmental organs become 

 compound, and may have as many as twenty funnels, etc. Both simple 

 and compound segmental tubes occur in all parts of the mesonephros, and 

 are arranged in no definite order. 



In the Anura (Spengel) all the segmental tubes are compound, and an 

 enormous number of peritoneal funnels are present on the ventral surface, 

 but it has not yet been definitely determined into what part of the seg- 

 mental tubes they open. 



