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neural longitudinal musculature, i. e. the lateral line, in which 
they are implanted. This line does not always lie exactly 
halfway between the two parapodia of one side but, e.g., 
at the beginning of the abdomen rises more to the dorsal 
side and at the end sinks more to the neural side, thus 
forming a slightly curved S. These knobs are provided 
in the centre with extremely fine sense-hairs. In this respect 
these sense-organs show an undeniable resemblance to those 
of Vertebrates: in both the central cells terminate in fine 
stiff cilia and are surrounded by so-called supporting cells. 
The number of sense-hairs is subject to variation in diffe- 
rent Vertebrates which possess lateral sense-organs, but is 
always considerably less than in Capitellids. Their length 
also appears to be less. Also in other families of polychae- 
tous and oligochaetous Annelids similar sense-organs have 
been described, while moreover the dorsal cirri of the ven- 
tral parapodia are considered homologous to them by EISIG 
(1887, p. 512), who in this respect follows KLEINENBERG. 
Metameric arrangement — Great weight is laid by EISIG 
on the metameric arrangement of the lateral sense-organs. 
In Vertebrates this is clearly pronounced in the ontogeny 
of Telosteans, and in other groups it is rendered probable 
by several observations. In part, the occurence of more 
than one sense-organ in one segment, is accounted for by 
the faculty of dividing which was first demonstrated by 
MALBRANC (1876) and afterwards confirmed by others. But 
only in Teleosteans a truly metameric arrangement of the 
sense-organs at their first appearance has been observed, 
which, however, is considered by some investigators as à 
secondarily acquired character. It is not impossible, that à 
primitive metameric arrangement of the lateral organs might 
have been gradually obscured when the external segment- 
ation, so strongly pronounced in the chitin-coated Annelids, 
became less distinct in Vertebrates, and only* in such cases 
might have been preserved, or have reappeared, where 
the integument shows metameric segmentation, as e@.g. In 
Siphonops and in Ichthyophis. and in Teleosteans, where the 
arrangement of the scales in general corresponds to that 
of the myotoms. 
Innervation.— If now we consider the innervation of the 
lateral sense-organs in Vertebrates and Annelids. it appears 
that this does not correspond in the two groups. In Capi- 
tellids the lateral organs from segment to segment are 
