8 FRANCIS H. WELCH, 
From the genital pit it passes directly inwards towards the 
centre of the segment at right angles to the edge. The cir- 
cumference of the organ is formed by a uniform band of 
circular and longitudinal muscular fibres +55 in. in thick- 
ness (fig. 7, d@). Tracing it from the bulb it is continuous 
along the long diameter, forming the outer cylinder, to the 
tip ; here it is seen to be reflected inwards lke the inflected 
end of the finger of a glove and to form a second cylinder 
(fig. 7, 9), +> Im. in diameter which passes backwards 
within the outer one, forming a bulbous dilatation (fig. 7, h) 
near the centre of the outer bulb, and is continued still further 
backwards by a convoluted tube similar in structure to itself. 
This convoluted tube (fig. 7, 2) lyimg within the outer bulb, 
and in Jength somewhat exceeding the entire penis, perforates 
posteriorly the outer bulb at its centre, and is continuous 
with the vas deferens or spermatic tube lying within the 
visceral space (fig. 7,7; fig. 1,9). Between the two mus- 
cular cylinders of the penis, and filling up the otherwise 
vacuum, are longitudinal muscular bands (fig. 7, 4). The 
internal cylinder is perforated down its centre by a narrow 
canal, which, constituting the aperture of the penis at its free 
end, passes along its long diameter and is somewhat dilated 
at the smaller bulb, hence is contained along the contorted 
tube and at length merges into the lumen of the spermatic 
duct ; this canal from the tip of the penis to the bulb is lined 
by ciliated epithelium.! From the external surface of the 
outer bulb posteriorly very strong muscular bands diverge, 
and passing in for some distance towards the centre of the 
segment are lost upon the inner surface of the boundary of 
the visceral space. Hence, then, it will be seen that there 
are muscular bands of the sheath, derived from the circular 
and transverse layers of the body structure, which would 
draw the bulb of the penis towards the genital orifice and 
at the same time lessen in depth, and possibly obliterate, the 
genital pit; there are those at the bulb posteriorly, as above 
mentioned, which would act in the opposite direction. It 
would also appear from the anatomical details that the entire 
penis could be bodily projected to the limits of the inflected 
preputial fold, =, in., but that further protrusion would be 
accomplished by the evolution of the inner cylinder, and to 
this end the convoluted tube within the bulb and the longi- 
tudinal muscular fibres of the outer cylinder are admirably 
adapted; while the muscular bands lying in the body of the 
penis between the cylinders and stretched by the protruded 
DE. SDP Macdonald, R N., F.R.S., informs me that he has observed 
the same ciliated-character on a protruded penis. 
