76 Observations upon the Habits, Structure and (February, 
sidedness can be seen only in the last plate, which is entirely 
uncovered. These muscles give to the body whatsoever of color 
it may possess, and probably also its metallic iridescence, although 
this latter feature may be due to the striz and fibres which 
exist in the integument. These muscles, from their very great 
extent as compared with the entire body, also give Amphioxus 
its remarkable power and activity in the sand and water, and from 
their similarity of arrangement at either extremity, enable, or 
rather compel it to move with that beautiful, elastic, line-of-beauty 
motion which is such an interesting feature of its progress. The 
transverse muscles lie in the walls of the abdomen and extend 
from the ventral edges of the muscle plates of either side to meet 
and unite in a raphe upon the median ventral line of the branchial 
sack. These muscles are nearly transparent in structure, and by 
their action serve to close the ‘sack walls upon or towards the 
. pharynx, as in the expulsion of water from the branchium by the 
branchiopore, and as is seen in all hardened or preserved speci- 
mens. The longitudinal abdominal muscles, which are found 
chiefly in the lower and posterior portion of the abdomen, proba- 
bly assist in the contraction of the abdominal walls, and also 
serve to shorten the sack and open the branchiopore. The mouth 
muscles, arranged in the walls of the buccal cavity and attached 
_ to the mouth ring and its appendages, serve to open the mouth, 
and by this operation unclose the overlapping oral tentacles. It 
has been said that besides these general muscles there are special 
muscles which serve to move each individual tentacle separate 
from the entire circlet. I have never seen any evidence of 
any such muscles, and never, in a single instance any indi- 
vidual motion of the tentacles, and if such muscles exist their 
action must be very feeble or entirely nugatory. The muscles of 
the pharyngeal ring are situated in the posterior portion of the 
buccal cavity and attached to the borders of the ring so as to 
bring the tentacles of these parts forward across the mouth of 
the pharynx. The sphincter muscles surround their respective 
orifices and serve, as in-the case of all sphincters, to approximate 
the edges of these different apertures. There may be a rudi- 
mentary sphincter to the anus, but neither in the young nor the 
adult have I ever observed what may be strictly called a closure 
of this orifice. 
Reproductive Organs—These organs consist of a number of 
roundish or oval bodies formed inside the lining membrane of the _ 
ue oe of the branchium and attached to the ‘oe a z the : 
