4, FRANCIS H. WELCH. 
riably lateral, and it was the rule to find it on the same side 
in contiguous segments, greatest number in such sequence 
7; while the exceptional was the alternating character, appa- 
rently so conspicuous a feature in the 7. soliwm, but rarely 
found in this species beyond two succeeding segments. In 
one instance only in this colony was the genital pore double, 
one on each side, yet malformations are far from uncommon, 
and with modifications of the normal textures subsequently 
to be detailed. With reference to the position of the genital 
pit in the lateral edge relative to the length of the proglottis, 
it occupied the centre from its first appearance to the naked 
eye to the 765th segment; and from this part of the colony, 
where the length and breadth of the individual components 
were equal, the orifice gradually became placed more and 
more below the central line, until ultimately it was seated in 
the lower third of the segment. ‘This gradual transposition, 
however, was due to changes going on in the upper half of 
the zooid, having for their end the separation of the function- 
completed segment from the parent stem, and in no wise 
dependent on alterations of the generative system, so that it 
may be stated, that the position of the genital pit in the 
lateral edge in this species up to maturity of the segment is 
decidedly central; the changes connected with the setting 
free of the lowermost proglottides will be subsequently 
described. Other naked-eye features of the lower halt of the 
colony were,—protrusion and tumefaction of the circumference 
of the genital orifice and unevenness and opacities of the flat 
surfaces of the segments from internal changes in the female 
generative system. Minor modifications of the foregoing 
rough details were observed in individual colonies, but the 
above fairly illustrate the general anatomical characters of 
the tapeworm as a whole. 
Turning our attention to the constituents of the individual 
four-sided flat segment, zooid, or proglottis, we may primarily 
divide them into (a) body framework, embracing skin and 
parenchyma with its muscular and inorganic elements, and 
(6) contained viscera, male and female generative systems, 
and water-vascular canals; first entering into a description 
of these individually, and subsequently detailing the modi- 
fications they undergo in the progressive development from 
the head end of the colony downwards. 
The skin (fig. 4) is composed of an epidermis and a corium; 
the former consists of a delicate imbricated epithelium layer 
=a'sy im. in thickness, the latter of a firm structureless elastic 
chitinous layer z,',5 in. thick, having on its exterior the 
epidermis, and on its interior a thin stratum of closely aggre- 
