42 THE YOUNG OF THE CRAYFISHES ASTACUS AND CAMBABUS . 



most are fastened to plumose hairs upon tlie pleopods of the second to 

 fifth somites inclusive, and some accoimt of these pleopods may be given here 

 in connection with questions as to how the eggs and larvae are attached to the 

 mother. 



The posterior face of the fourth left pleopod of a female about to lay is 

 represented in figure 44. It will be noted that the endopodite is longer than 

 the, exopodite, and both bear a fringe of long plumose setie on their right and 

 left edges. The setiB are shorter toward the base of the exopodite and of the 

 endojiodite while on the protopodite there are but a few plumose setae in two 

 tufts upon the inner edge. The long set:e make of the pleoj^od a wide fan or 

 flat brush since the set:i3 lie close together and like the wing feathers of a l)ird 

 form a rather fiat firm expanse. The protopodite has a basal part containing 

 several calcified plates in a soft membrane, and a long segment that is well 

 calcified except for a triangular soft area toward its base on the posterior face. 

 The endopodite is made of two segments and the exopodite of one. The endopo- 

 dite and the exopodite are also somewhat annulated in appearance owing to 

 the grouping of the cement glands. The groups are opaque white and from each 

 side tend to rvm together across the posterior face. Distally they do not meet 

 but proximally they meet and make cross bands. Still farther toward the base 

 the glands cover the entire surface more and more completely. The non-gland- 

 ular areas are clear and not opaque, and in the figure are represented dark. 



The anterior face differs from the posterior (fig. 44) in a greater de- 

 velopment of glands which formed transverse bands more nearly all the way to 

 the ti]). As so many of the glands are to the right and left near the setas, they 

 are well placed to smear their seci-etion over the seta?. 



Toward the tips of the pleopods the exoskeleton is so translucent that with 

 Zeiss 2 D, the striation of the muscle fibers, the branched connective tissue 

 cells, granular blood corpuscles, and the polygonal gland cells may be seen. 

 The gland cells are about the diameter of a muscle fiber and larger than a 

 blood corpuscle. 



In most eases the j)lumose sette spring from over the glands, and the base 

 of a seta is as thick as two gland cells. The set:e have a large central cavity 

 and a thick wall which is highly refractive and clear and is of unequal thick- 

 ness so that it projects into the cavity in lumps or waves, and gives the distal 

 part of the axis of the seta a somewhat segmented aspect. At the base each 

 seta is articulated to the exoskeleton, and its central cavity is constricted by a 

 clear refractive thickening of the wall that leaves very little communication be- 

 tween the cavity of the seta? and the cavity of the body. 



The side branches of the seta spring out not only along its sides but also, 

 scatteringly, along its posterior face so that the ])lum()se seta is more like a 

 bottle briLsh than like a flat feather, ^\'hile the side branches generally make 



