new Species of Thamnodrilus. 157 
description of the typhlosole in Th. columbianus * shows that 
there must be a considerable similarity between the two 
species here compared. But his description is not full, and 
it would appear that in Th. columbianus the organ begins in 
segment 18 with the commencement of the large intéstine. 
In a few other species Michaelsen has noted the large size of 
the typhlosole; in 7. huwald, for instance, it is longer (in 
transverse section) than the diameter of gut, and thus lies 
in a bent position, while in Th. friderict it is also big and 
curved like the letter “ 87’ T. 
It is interesting to note that in a transverse section of the 
typhlosole of Th. cognetti the axis is seen to run in a zigzag 
of several curves, thus producing the lateral dilatations. But 
the curve cannot be unravelled, the walls of the several parts 
adhering and being fused. The mode of origin of this 
peculiar typhlosole is perhaps thus shown—i. e., a simple fold 
curved upon itself several times for the purpose of stowage. 
A subsequent and more complete fusion between the various 
layers would produce a central axis and lateral outgrowths. 
Such a metamorphosis would therefore produce the complex 
typhlosole of Hormogaster f. - 
As in other species of the genus, the dorsal vessel of 
Th. cognetti is dilated in certain segments and with unequal 
dilatations. There are five of the swellings of the dorsal 
vessel altogether, which lie in segments 15-19. 
Those of 15 and 16 are not very marked ; those of 17 and 
18 are much larger, while that of 19 is again not very large. 
The dorsal vessel suddenly narrows to its usual dimensions 
in segment 20. The dntestinul hearts are in 10 and 11, as in 
so many species ; I do not think that there was a pair of 
hearts in 12, but in so poorly preserved specimens I am 
unwilling to be quite certain in statement. The two pairs 
mentioned are pear-shaped, dorsally suddenly diminishing to 
anarrow “stalk,” which is their communication with the 
supra-cesophageal trunk. 
The most anterior nephridia lie along the sides of the 
cesophagus, and are large and conspicuous “ peptonephridia.” 
The next pair appeared to be in segment 5, and thereafter 
these organs were to be found in every segment. The ante- 
rior nephridia, as is usual in the genus, have no cecum, 
* Zool. Jahrb. t, c. p. 185. 
+ Loe. cit. p. 148. 
} Rosa, “Sulla Struttura dello Hormogaster redii,” Mem. R. Ace. Sci. 
Torino, xxxix. 1888, fig. 3 of plate. 
