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. xxxiii 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 taU. 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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