112 MEMOIES OF THE NATIONAL ACADEMY OP SCIENCES. 



Along the edge of this layer are seen to lie more or less free cells, filled with a dense protoplasm. 

 In other portions the connective tissue cells are elongated, more or less polygonal or fusiform, 

 empty of protoplasm, their walls somewhat irregular and shriveled, with small nuclei (Fig. 3 c). 

 These cells are either crowded and their outlines indistinct (3 e), or the tissue is looser and the cells 

 more polygonal (3 c). It will be seen by the sketches that the space in normal Cambari occupied by 

 the rods and retina is filled in with this packing of loose connective tissue. 



The optic ganglion survives in the blind crayfish, but it is difficult to homologize the different 

 portions of the white or myeloid substance with that of the normal-eyed crayfish or lobster. By 

 reference to Figs. 3 a and 3 ft it will be seen that the fibers of the optic nerve pass into the bulb-like 

 optic ganglion, and beyond are three much smaller lobes, and in Fig. 3i»a fourth smaller lobe. 

 Whether these smaller lobes represent the inner and middle black pigment layer of the retina of 

 the normal eye or not is difficult to state. These fine lobes or subdivisions of the central " puntz- 

 substanz " or myeloid substance is enveloped by a layer, varying in thickness, of ganglion cells. 

 The envelopiug mass is sometimes ten cells deep. The distal end of this layer is prolonged so as to 

 reach the hypodermis at the end of the eye, as at 3 a, 3 b, a. The ganglion cells are remarkably small 

 and of very uniform size, their nuclei beiug no larger and with the same shape as the hypodermis 

 cells. A few are represented at Fig. 3 d ( x 225 diameters). Only one as large as that indicated by 

 the x was observed, whereas in the lobster's optic ganglion there are many with a diameter three 

 times as great. The ganglion cell-walls are indistinct, being in general broken down and rendered 

 obsolete. The nuclei are very distinct, ami take the stain well, while the nucleoli are composed of 

 a number (sometimes a dozen) of small granules. The ganglion cells send nerve fibers into the 

 myeloid substance, which is evidently, when seen in sections, the transversely-cut ends of such 

 fibers passing in from all sides. 



The muscle which moves the eye is well developed, as seen in Fig. 3-3&, mus. 



To recapitulate: In both the species of American blind crayfish: 



The integument of the eye, with its stalk, is present, but abnormally lessened in size. 



The optic nerves and optic ganglia are p resent, but the latter are small and degenerate. 



The facets and entire cornea, the cones and rods, and the three black pigment layers are 

 totally abolished. 



It will be seen that this is nearly the reverse of what takes place in Cseeidotsea, where the pig- 

 ment mass and cones, as well as facets, may in certain individuals be retained, while the optic 

 nerves and optic ganglia are the first to be abolished. 



THE BRAIN AND RUDIMENTARY EYES OF BLIND MYRIOPODS. 

 (Pis. XXIV, XXV.) 



A great deal of interest attaches to Newport's work on the brain of Myriopods, because he has 

 figured dissections of the brain of certain eyeless species both of Cliilopoda and Diplopoda. From 

 his researches it appears that the brain of the eyeless Geophilus, as well as Polydesmus, is want- 

 ing in optic ganglia and optic nerves, only the procerebral and antennal lobes remaining. 

 (PI. XXVII.) 



The drain of Chilopod Myriopods in general. — From the examination we have made of microscopic 

 sections of the brain of Bothropolys and Cermatia, as well as the forms described below, the 

 Myriopod brain is closely homologous with that of winged adult insects; differing, however, in 

 wanting the calyces and their stalks ; i. e., the so called mushroom bodies, and perhaps the so-called 

 "central body." In Cermatia (PL XXIV, fig. 1) the optic ganglia are large and unusually well 

 developed, the eyes being compound and larger than in other Myriopods. The general structure 

 of the myeloid substance, its proportions to the investing ganglion cells, the size of the procerebral 

 lobes and their relations to the optic and commissural lobes are as in insects. 



Iu Bothropolys, a genus closely allied to Lithobius, the optic ganglia are large and well 

 developed, becoming contracted at the origin of the optic nerve, which gradually increases in size 

 toward the eyes, as seen in PL XXVI, fig. 2. 



