DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 499 
possible to confound the two species. Besides, the dorsal 
vessel is not completely double in Acanthodrilus nove- 
zelandiz. The two tubes, as I have already pointed out 
(7), in the latter species become fused at the septa; 
whereas in Acanthodrilus multiporus they retain their 
distinctness at the septa as elsewhere. 
In Acanthodrilus multiporus the prostomium is small, 
and does not divide the buccal segment ; the anterior segments 
are so much divided into annuli that their limits are almost 
impossible to map by a superficial inspection of the worm ; 
there are also internal structural differences of importance, 
particularly in the nephridial system, between the two spe- 
cles. 
The transparent cocoons allowed the dorsal vessel to be 
quite plainly visible, and it showed the complete double cha- 
racter which has just been referred to; the mature embryos 
extracted from the cocoons showed the other external charac- 
ters which serve to discriminate the species. As the cocoons 
were all perfectly similar I have no doubt that they all belong 
to this species. 
Mr. Smith informs me that “ the cocoons were found on the 
edge of a swamp, which is now quite dried up owing to the 
long drought ; in other seasons there are generally several feet 
of water covering the spot where we obtained them. I ob- 
tained a few (some of the more advanced) among the loose 
shingly soil, from which the water had subsided.” 
§ The Cocoon. 
Our knowledge of the cocoons of earthworms is at present 
almost confined to the indigenous Lumbricide. A very good 
summary of our knowledge upon this point, together with 
many new observations, is to be found in Professor Vejdovsky’s 
‘ Entwickelungsgeschichtliche Untersuchungen,’ Heft 1. 
The only exotic form which has been as yet described is 
Megascolex ceruleus, of which I myself have given an 
account (8). It is clear that the cocoon of that species, as 
Vejdovsky has pointed out, departs in no essential particular 
