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POPULAR SCIENCE REVIEW. 
placed month, an alimentary canal, and a large flat expanse of 
body (always carrying the eyes) in front of the mouth — to form 
the proboscis, you must draw out this prseoral region to a 
length sometimes equal to that of the whole animal, arm it in 
some cases with stylets or spines, and tuck the muscular tube 
thus formed into the body, making it overlie the alimentary 
canal, as the finger of a glove might be tucked into its hand. 
Thus you may conceive the “ proboscis ” of Turbellarians to be 
formed, with muscles so that it can be drawn in and out at 
pleasure. Its doubtful use has caused various mistakes. Many 
have not got it, but only an expanded or simpler modifica- 
tion of the prseoral region (Dendroccel Planarians); all the 
Nemertians, however, are thus armed, and many of the Rhab- 
docoel Planarians. De Quatrefages regarded the proboscis of 
Nemertians as the alimentary canal, no doubt reminded by it 
of the eversible pharynx which the marine Annelids possess. 
Oersted took it for the main organ of copulation, led into this 
error by the frequent presence of little hard spines, which are 
also found in the penis of some Turbellaria (Opistomum). 
Leuckart was one of the first to recognise the presence of the 
proboscis in the straight-gutted Planarise, in which most of all 
there had been a eonfusion with the mouth (even till within 
the last three or four years), and now the latest and most 
reliable writers (e. g. Victor Carus) are of his opinion. 
The nervous system of Turbellarians is very simple ; it con- 
sists essentially of two large ganglia placed in front (often very 
far in front) of the mouth, and joined by a short sort of commis- 
sure, which passes always over the dorsal surface of the proboscis 
when it is present. Twigs pass in various directions from these 
ganglia, two principal lateral stems being often present. There 
is no representative of the cord and ganglia placed beneath the 
alimentary canal which is found in Annelids and Arthropods. 
The eyes , which are very simple, often only pigment spots, 
vary in number from two to sixteen or more ; and being always 
close to the great ganglia (the equivalents of the sensory or 
supra- oesophageal ganglia of higher animals), are always in 
front of the mouth. In some Turbellarians a supposed audi- 
tory capsule is present, and the Nemertians are peculiar in 
possessing two ciliated clefts in the prseoral region, which may 
be sensory. Th q vascular system is closed in adult Nemertians, 
and contains red blood in some species ; in Planarians, its stems, 
which are disposed laterally, communicate by two or more con- 
tractile apertures with the exterior, and water is thus admitted. 
We have now to speak of the generative organs and methods 
of reproduction and development in these creatures ; and here a 
word may be said as to the strange and anomalous position of 
the mouth in relation to the fore and hind extremities, and the 
