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THE TELSON OF THE MACRUROUS CRUSTACEA. 93 
13. ON THE TELSON OF THE MACRUROUS 
CRUSTACEA.* 
Tue relations of the telson of the lobster and its allies are so 
variously regarded by zoologists of the present day, that no apology is 
needed in bringing forward any facts which tend to settle the point. 
By Milne-Edwards it is considered as a seventh abdominal segment ; 
but I cannot find in his writings any reasons given for his belief. Van 
Beneden is also stated by Professor Rolleston to hold the same opinion. 
Professor Huxley considers the telson an azygos appendage, and not a 
true segment of the body; and Professor Rolleston agrees with him, 
stating that it only carries appendages in one or two cases, whereas it 
is a law common to all Crustacea, that every segment has its ap- 
pendages. 
An attempt will be here made to show that in a specimen of 
Scyllarus arctus, in the Zoological Museum of the University of Cam- 
bridge, there is sufficient evidence to prove that the telson is a true 
body segment, and that it is provided with true segmental append- 
ages, though the nature of these is somewhat modified by cohesion 
and adhesion. 
In this specimen the sizth abdominal segment is in the main 
similar to that in the lobster, but its dorsal surface is grooved instead 
of plain. The infero-lateral terminations of its dorsal shield are 
slightly recurved and not sharply pointed, those of the first abdominal 
segment being decidedly so, but the acumination becomes less marked 
in each succeeding one. The swimmerets are greatly developed, the 
propodite not exhibiting any decided spinous protuberances. Both 
the exo- and the endo-podite, which are expanded horizontally, are 
composed of two, a proximal calcified and a distal fin-like portion ; 
the anterior margin of the former in each of these segments being 
prolonged outwards in the form of a spine. The distal fins are com- 
posed of a translucent membranous substance supported on a radiating 
framework. 
At the attached extremities of the anterior and posterior margins 
of these fins, there are small elongated calcified masses, which seem to 
be the points at which their delicate structures come in contact with 
one another and the neighbouring parts. 
Ventrally there is a transverse calcified bar, concave forward, 
* “ Journal of Anatomy and Physiology,” V. pp. 270-3. May, 1871. 
Page 271. 
Page 272. 
