32 PEOGRESS OF MICROSCOPICAL SCIENCE. 



Crangon maculosus, in wliicli there is no metamorphosis. The embryo 

 is a Nauplins ; it sheds a Nauplius skin about the middle of embryonic 

 life. This Nauplius skin corresponds in some respects to the " larval 

 skin" of German embryologists. The recently hatched young of 

 Limulus can scarcely be considered a Nauplius, like the larva9 of the 

 Phyllopoda, Apus, and Branchipus, but is to be compared with those 

 of the trilobites, as described and figured by Barrande, which are in 

 Trinucleus and Agnosius born with only the cephalothorax and pygi- 

 dium, the thoracic segments being added diu'ing after-life. The cir- 

 cular larva of Sao hirsuta, which has no thorax, or at least a very 

 rudimentary thoracic region, and no pygidium, approaches nearer to 

 the Nauplius form of the Phyllopods, though we would contend that it 

 is not a Nauplius. The larva passes through a slightly marked meta- 

 morphosis. It differs from the adult simply in possessing a less num- 

 ber of abdominal feet (gills), and in having only a very rudimentary 

 spine. Previous to hatching, it strikingly resembles Trinucleus and 

 other trilobites, suggesting that the two gi'oups should, on embryonic 

 and structural grounds, be included in the same order, especially now 

 that Mr. E. Billings has demonstrated that Asaphus possessed eight 

 paii'S of five-jointed legs of uniform size. The trilobate character of 

 the body, as shown in the prominent cardiac and lateral regions of the 

 body, and the well marked abdominal segments of the embryo, the 

 broad sternal groove, and the position and character of the eyes and 

 ocelli, confirm this view. The organization and the habits of Limulus 

 throw much light on the probable anatomy and habits of the trilobites. 

 The correspondence in the cardiac region of the two groups shows 

 that their heart and circulation was similar. The position of the eyes 

 shows that the trilobites probably had long and slender optic nerves, 

 and indicates a general similarity in the nervous system. The genital 

 organs of the trilobites were probably very similar to those of Limu- 

 lus, as they could not have united sexually, and the eggs were probably 

 laid in the sand or mud, and impregnated by the sperm-cells of the 

 male, floating free in the water. The muscular system of the trilobites 

 must have been highly organized, as in Limulus, as like the latter they 

 probably lived by bm-rowing in the mud and sand, using the shovel- 

 like expanse of the cephalic shield in digging in the shallow palaeozoic 

 waters after worms and stationary soft-bodied invertebrates, so that we 

 may be warranted in supposing that the alimentary canal was con- 

 structed on the type of that of Limulus, with its large, powerful 

 gizzard and immense liver. 



American Microscopy. — At the last meeting of the American Asso- 

 ciation, that body taught the British Association a useful lesson in 

 forming the subsection of Microscopy. In this department much 

 valuable work was done, which we shall occupy the rest of our number 

 in reporting : — 



A New Form of Binocular Microscope, by President F, A. P. 

 Barnard, of Columbia College, N.Y., who described elaborately a 

 newly contrived instrument in which the light is separated into two 

 pencils by double refraction, and which cannot fail to be a valuable 

 addition to the resources of the working microscopist. 



