402 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



poor success attended our efforts. The brain lies, as seen in fig. 2, in 

 ttie midst of the liver, and in the process of cutting- through the head 

 the brain slips aside from or crumbles before the edge of the razor. Of 

 course the only proper way is to remove the brain from the living animal 

 and properly prepare it for the microtome ; but this is next to impossible 

 owing to its small size. Indeed, the difficulties in the way of making a 

 good dissection of the brain of these creatures, particularly Apus, are 

 very great. After working for some time at the brain of well-preserved 

 Apus lucasanus, we were able to satisfy ourself that the drawings and 

 descriptions of Zaddach in his classical work on Apiis cancriformis are 

 correct, although his drawing of the entire ventral chain (his Tab. Ill, 

 fig. 1) might be improved; his representations of the brain are undoubt- 

 edly correct enough for all practical purposes, and we have copied in 

 Plate XXXII three of his excellent figures. The figure of the entire 

 nervous system oi Apus lucasanus (Plate XXXII, fig. 1) was drawn by 

 Mr. Kingsley, and adopted with some important corrections in the posi- 

 tion and form of the brain. The sketch is necessarily in part diagram- 

 matic, and no nerves to the appendages are represented. As seen in 

 the copies of Zaddach's figures the brain is small, situated right under 

 the compound eyes, and it innervates only the simple eye or ocellus 

 and the compound eyes. The nerves to the two pairs of antennae, fig. 5 

 {ant^, ant^), arise from the commissures, and not from the supraoesoph- 

 ageal ganglion. The rest of the nervous cord is ladder-like. 



In the BrancMpodidce the nervous system shares with the other sys- 

 tems of organs in a general advance to a higher plane of organization. 

 According to Clans excellent figures of the brain, especially of the very 

 3^oung Branchipus stagnalis, the nerves to the first and second antennas 

 arise from groups of ganglion-cells situated on the outside of the com- 

 jnissures, the ocellus and two stalked eyes being innervated from the 

 brain as in all other Phyllopods, and it will probably be found that in 

 the early stages the commissures are jirovided with ganglionic enlarge- 

 ments from which the appendages of the head are innervated ; thus there 

 may be a slight resemblance in this respect to the ganglionic (esophageal 

 ring of Limulus. 



We have, then, in the suboesophageal ganglion of all the Phyllopods 

 a simple, small ganglion, no more differentiated than those forming a 

 part of the ventral cord. Plate XXIII, fig. 1, gives a vertical view of 

 the brain of the adult Artemia, which is nearly continuous with the 

 optic ganglion. On Plate XXXIII, fig. 8, is represented a section of 

 the small brain of Branchipus vernalis. It is very simple in structure, 

 the ganglion cells small, scattered, and indistinct. Fig. 8a shows the 

 ganglion cells enlarged. No fibers appear, though more careful ob- 

 servations than I was able to make are needed before we can have a 

 complete knowledge of the brain of the supraoesophageal ganglion in 

 the Phyllopods. 



For the structure of the abdominal jiortion of the nervous cord the 

 reader is referred to Leydig's account and his figure in Tafeln zur Yerg. 

 Anatomic, Taf. Y, fig. 5. 



It is apparent, however, that in the Phyllopoda the brain is a very 

 simple affair, and not much higher in complication of structure than the 

 brain of worms, and when we compare it with the brain of the Decapods, 

 or at least that of the crayfish and lobster, these alone having been 

 studied, we are comparing two very different organs. The brain of the 

 Decapoda is an aggregate of at least two pairs of ganglia besides the 

 primitive pair innervating the eyes. The extreme degree of cei)haliza- 

 tion, by which the head becomes more compact and homogeneous, has 

 had its resultant effect upon the primitive brain and the ganglia behind 



