ON SHEPHEARDELLA, A NEW TYPE OF MARINE RHIZOPODA, 131 
Shepheardella t^niformis. — Nov. Gen. et sp. 
General description . — The body of the Rhizopod is uni- 
cellular, elongated, and abruptly pointed at both ends. Flat- 
tened and ribbon-like when in a state of activity, rounded 
and worm-like when at rest. It is furnished with a flexible, 
transparent, colourless integument of considerable flrmness ; 
and the whole tubular cavity is densely filled with yellowish, 
coarsely granular protoplasm, having a very distinct oval nu- 
cleus, and occasionally also a few scattered non-contractile 
hyaline vesicles. Thesarcode rotates in a regular stream around 
the interior of the integument, and carries the nucleus along 
with it ; the current performing a complete circuit within the 
cell. The nucleus is seldom carried entirely round the cell, 
being as a rule intercepted in its course along one stream 
and passed over into the opposing one before it has travelled 
far from the centre in either directions. The opposing 
streams of sarcode thus formed on the two sides of the cell, 
are not separated from each other by any clear line as in 
Characece, though otherwise much resembling the pheno- 
menon observable in the living vegetable cell. The prin- 
cipal difference between the two is in the direction of the 
current, that of Chara advancing in a spiral direction, whilst 
that of Shepheardella completes its circuit in one plane, the 
two currents slightly overlapping each other. The in- 
tegument is perforated at each end by a minute aperture, 
through which’ some of the sarcode passes and collects into a 
small mass. From this mass a very delicate coating spreads 
over the whole exterior surface of the integument, and this 
thin layer occasionally throws out a pseudopodium. But 
the great network of inosculating and branching pseudopodia 
are at the two extremities of the organism, extending them- 
selves from the terminal masses of sarcode to a distance 
considerably exceeding the whole length of the body, as in 
PI. XV, fig. 2. The circulation of the finer granular sar- 
code in the pseudopodia is easily traced. It is very rapid, 
advancing and returning in single, double, or even triple 
streams, according to the breadth of the pseudopodium 
traversed. So that from the rotation of the chief mass of 
sarcode within the test and the external circulation in the 
pscudopodia, it is evident that every part of the body- 
contents, the nucleus excepted, is in turn brought in contact 
with the surrounding water. The combined movements 
present an evidence of vigorous life rarely exhibited among 
the Rhizopoda, and the transparency of the “test^* permits 
the internal functions of the organism to be as easily followed 
as the external. 
