ECONOMIC RELATIONS, ANATOMY, AND CIFE HISTORY OF GENUS LERN^A. 1 77 



Owing to the torsion of the body only the anterior pair of legs lie symmetrically 

 upon the median line. The others are carried more and more to the right or left until 

 the fourth pair come to lie apparently on the side of the body, or may even be twisted 

 so far that they appear to be on the dorsal surface. Really, of course, all the legs are 

 on the ventral surface, and we must conceive of the longitudinal axis as twisted equally 

 with the body itself. The apparent position of the legs thus affords a ready means of 

 measuring both the direction and the amount of the torsion. (See fig. 68, 75, pi. xiv.) 



The abdomen. — This is a short blunt cone on a level with the dorsal surface of the 

 genital segment and ending in two minute anal laminae. (See fig. 69, pi. xiv.) 



These are so tiny that they escaped the notice of all the earlier investigators but 

 are very distinct, and each is armed with a long plumose seta with a much shorter 

 nonplumose one on either side of it. 



The abdomen shows no other processes or appendages. 



INTERNAL MORPHOLOGY. 



The skin. — The integument is made up of three layers, the outer one hard, the two 

 inner ones soft. In the present genus the outer layer never becomes really chitinous, 

 as it does in some of the other Lemaeids {Hcemobaphes, LertuBolophus, etc.). It is yel- 

 lowish brown in color and offers considerable resistence to the penetration of fijcatives. 



It shows in a cross section (fig. 8, pi. vii) that it is made up of thin layers of lamellae, 

 many (7 to 10) of which are packed together one over another. These lamellae lie in 

 contact with one another and show no such intervening spaces as were noted in one 

 instance by Hartmann. Neither do any of the species examined by the present author 

 show the delicate surface markings seen by Hartmann on the outer lamella of L. barnimii. 

 But it should be added that Hartmann examined living material while in the present 

 instance only preserved material was used. 



This lamellar layer of the integument is perforated by pore canals (pc), which are 

 more numerous in the center and posterior portions of the body and less numerous at 

 the anterior end and on the horns and appendages. 



Each canal is a tolerably thick-walled tube, the outer surface of the walls being 

 finely wrinkled transversely, while the inner lumen is perfectly smooth. The outer 

 and inner openings of the canals are slightly larger than the central lumen, and in the 

 posterior body and horns the external surface of the canals at the outer opening forms 

 a six-sided polygon around the circular lumen, as stated by Hartmann. 



The pregenital prominence. — In lateral view this prominence forms a sort of heel, 

 the abdomen a sort of toe, while the free thorax is the leg of the boot, as was first sug- 

 gested by Nordmann. Claus stated that in L. esocina the posterior part of the body 

 first assumed the boot-shaped bending at the begiiming of sexual maturity. He ought 

 rather to have said at the completion of sexual maturity, for as we can see from the 

 life history here given sexual maturity begins and becomes so far developed as to allow 

 of impregnation during the copepodid stage, while the boot shape is not assumed until 

 the creature has reached its maximum length. (See fig. 68, pi. xiv.) 



Inside of this external layer of the integument is a single, comparatively thin layer 

 of polyhedral cells {hy), whose walls and nuclei are very clearly marked. This is the 

 first of the inner soft layers and corresponds to the "hypodermis" of Claus or the "chi- 

 tinogen layer" of Hartmann and other authors. It is much softer than the outer layer, 

 the cell contents are fine grained, and both nuclei and nucleoli are distinctly visible. 



