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of Edinburgh, Session 1868 - 69 . 
entiated than in the Enopla. The young in the most conspicuous 
Families undergo a remarkable metamorphosis. 
In this Sub-Order there are several Families, the most conspicuous 
and typical of which is that of the Borlasidse, characterised by the 
more or less elongated shape of the ganglia, the arrangement having 
with the commissure the form of a horse-shoe. The muscular 
covering of the body is composed of three layers— external longi- 
tudinal, circular, and internal longitudinal. The proboscis is 
furnished with five coats, viz., external elastic, external longitudinal 
and accessory bands, circular, basement, and glandular layers. The 
circulatory system consists of three great longitudinal trunks, two 
lateral and a dorsal, which frequently anastomose by transverse 
branches, form a rete mirabile in the oesophageal region, and unite 
in lacunae behind the ganglia. Head, with deep lateral fissures in 
connection with the cephalic gland, which is rounded, and not 
furnished with long tubes or ducts. 
A curious specimen from Herm forms the type of a group that 
would require to be raised to the rank of a Sub-Family, but as only 
one specimen has yet been found, it is thought advisable to post- 
pone this at present, and distinguish it only generically. In this 
animal the proboscis is extremely slender in proportion to the bulk 
of the body, and in its minute structure differs from the type of the 
Borlasidse in having no accessory bands cut off from the longitudinal 
layer. Externally the organ has an elastic investing layer, then a 
longitudinal, within which are a thin circular and a glandular coat. 
The reddish colour of the muscles of this species, and the tinted 
circulation, are likewise quite characteristic. 
A more distinct Sub-Family of the Borlasidse than the foregoing, 
perhaps, is that of the Borlasian without lateral slits. The anatomy 
of the body-wall agrees with Lineus, but there are no cephalic 
fissures. The structure of the proboscis is also characteristic, for 
there is externally no distinct investing layer, the outer coat con- 
sisting of spiral and interwoven muscular fibres, the middle of 
longitudinal, and the internal of the usual glandular coat. 
The Meckelidcz constitute a very distinct Family of this Sub- 
Order. The general structure of their nervous system agrees with 
Borlasia, but the lateral nerve-cords are placed between the circular 
(external) and the longitudinal (internal), these being, moreover, 
