94 Mr, E. Kay Lankester on the Organization 



this species, consequent on the observation of the last species, 

 has shown me that in T.rivulorum there is a r^^dimentary weh 

 to the dorsal setse of the first ten fasciculate segments, and 

 even traces of such a web as far as the fifteenth. This and 

 the peculiar form of these setge has not before been described. 

 Though considerably smaller relatively, yet the set£e in this 

 region approach those of T. umhelUfer also in form, having 

 the form seen in Z», 5', fig. 2, with the prongs nearly straight, 

 unlike those of the ventral region and of the other parts of the 

 body (a, fig. 2) . It requires a glass of very good power to see 

 this web well — a -yV or Hai^tnack's 10 a immersion. It is 

 most developed in the setse of the sixth and seventh fascicles, 

 and is to be made out, though very slight, in the setje of the 

 fourteenth fascicle, where the prongs ha-ve assumed the unci- 

 nate form characteristic of most Oligochsetous crochet-bristles. 

 A remarkable fact is, that in young [i. e. small) specimens of 

 T. rivulorum the webbing of the bifurcation of these bristles 

 is more obvious than in the older and larger individuals. 

 This suggests the sujiposition that T. umleUifer represents a 

 more primitive fonn, and that the rudimentary webbing 

 of the setse of T. rivulorum is a case of retention, in a rudi- 

 mentary state, of ancestral characters which were formerly 

 highly developed. When it is remarked, further, that such a 

 form of seta is unknown except in marine Annelids, and that, 

 as far as it appears, T. umhellifer is a hrackish-ioater form, the 

 rudimentary webbing in T. rivulorum becomes more important. 



I have seen no trace of such webbing in the setge of Limno- 

 drilus (which is consequently thus further separated from 

 Tuhifex)^ nor in any other Oligochsetous Annelid examined 

 with care for this pur[30se. 



Four or five very fine hairs, of six times the length of the 

 setge, are often to be seen, in small specimens of Tuhifex^ sur- 

 rounding each seta near its apex ; they apparently result from 

 the splitting-up of the homy substance of the seta ; and they 

 occur in Nais as well. Small dark particles are placed at in- 

 tervals along these fine hairs. These appearances are proba- 

 bly pathological, but are so common as sometimes to lead one 

 to suppose them characteristic and normal. 



4. Enchytrceus and Pachydrilus. — In a garden-heap I have 

 obtained specimens of the typical Enchytrfeus vermicularis ; 

 whilst from a pond at Hampstead, from a running stream, 

 and from the Victoria Docks I liave obtained worms which 

 should be referred to Enchytrceus^ but possess blood coloured 

 red by haemoglobin. That from the Hampstead pond is 

 marked with light-yellow bands externally, and is otherwise 

 colourless. There does not seem to be sufficient ground for 



