394 E. W. MACBRIDE. 
In nearly all cases there is a small portion of this tissue also 
derived from the ventral pocket; this projects, as we have 
seen, into the niche left between the tooth and body of 
the primary skeleton. 
Professor Spengel gives a detailed description of the mus- 
cular system. It gives characters which are of great use from 
a systematic point of view ; but here we need only notice a point 
or two of general interest. There is no dermis of con- 
nective tissue; immediately beneath the epidermis is a 
basal membrane of cuticular substance, and this serves for 
origin and insertion of the muscles. 
Fig. 8 (Pl. 29) shows the arrangement of the longitudinal 
muscles in the proboscis. As there is an outer circular layer, 
it follows that the longitudinal fibres must insinuate themselves 
between the fibres of this to be inserted in the basal membrane 
of the ectoderm. Besides these fibres there is a median plate 
of dorso-ventral muscles, which make up the main mass of the 
median septum separating the two ventral pockets of the pro- 
boscis cavity. These do not cease, however, at the dorsal 
edge of this septum, but are continued right to the mid-dorsal 
line. The interesting point, however, is that the antero- 
posterior extent of this plate is correlated to the length of the 
head of the notochord ; hence the notochord in front of the 
skeletal rod appears to have a supporting function, and many 
of these fibres are, in fact, inserted in its basal membrane. 
Fig. 9 shows the relation of the muscles of the anterior face 
of the collar region to the skeletal rod. Spengel has made 
some very interesting observations on the habits of Balano- 
glossus. From these it appears that the animal progresses by 
burying itself in the sand and passing the sand through its 
alimentary canal, and hence that locomotion and nutrition are 
effected by one and the same process. It further appears that 
it is the proboscis and collar which are the active agents in 
locomotion, the rest of the body being dragged passively 
behind. Hence we can understand why the muscular, nervous, 
and skeletal systems should be so highly developed in the an- 
terior part of the body, and also why the animal should be 
