Chapter VI.— ANATOMY OF THE LOBSTER, WITH EMBRYOLOGICAL AND 
PHYSIOLOGICAL NOTES. 
Both the lobster and the crayfish have long been regarded as classical exponents of a 
zoological type and have figured so prominently in text-books that the elementary facts 
of the anatomy of few invertebrates are better known; yet there is still a wide field for 
more exact research in nearly every direction, as we have found whenever it was possible 
to dip below the surface. In the present chapter it will be necessary to restate certain 
elementary facts, but my embarrassment would be greater were this work intended solely 
for professional zoologists, who will probably find more that is new in the chapter which 
follows. 
In attempting to give a fairly consistent account of the lobster’s anatomy I shall 
not hesitate to enter into details, but shall endeavor to emphasize those parts of most 
zoological interest from the standpoint of morphology, physiology, and development. 
Numerous anatomical drawings are given, including the entire series of adult appendages, 
which may serve for more exact comparisons with the larval stages than have been 
possible hitherto. 
THE BODY. 
The lobster’s body (pi. xxxm and table 4), which the fisherman compares to a pistol 
in shape, but holds by the “barrel,” is made up of a series of 21 somites or body segments 
(or of 18, omitting 3 of doubtful value), all but the last of which bear paired and jointed 
appendages. The first 14 are united into one piece called the cephalo-thorax or “barrel,” 
while the last 7 form the flexible abdomen or tail. This primitive segmentation which 
is expressed chiefly in the exoskeleton or the hard and soft skin extends also to the 
nervous system, as well as to certain muscles and blood vessels, but does not involve 
the soft parts of the body as a whole. A cuticle, which is strengthened with lime and 
other minerals to form a hard crust wherever greater protection or rigidity is needed, 
follows every inward fold of the skin and covers every part of the body down to a micro- 
scopical hair. 
The skeletal parts of head and thorax are fused on the upper and lateral surfaces 
to form a large cephalo-thoracic shield or carapace, often called simply the “shell,” 
which is “buttoned” on to the tail by small overlapping pleura of the first small somite 
of this part. The carapace is marked and sculptured in a very definite manner by 
symmetrical folds or grooves, tendon marks, and absorption areas, not to speak of pro- 
tective spines, and smaller tubercles, fringing sensory hairs, and the very minute depres- 
sions with which it is stippled all over, the hair pores to be later described. The light 
median stripe which runs, as if drawn with pen and rule, from the rostrum to the hinder 
border of the carapace represents an absorption area of the greatest importance to the 
molting lobster. A prominent fold known as the cervical groove crosses the carapace 
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