314 MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



He then adds : 



The par' of the brain formed by the external groove becomes the optic ganglion of the lateral eyes, as in the case 

 of the spicier. The optic ganglion of the median eyes is produced from the epiblastic thickening forming the united 

 mouth of the invagination for the median eyes (Fig. 69, g. med. e., our tig.). 



The brain, which was ahnost circular in its outline, as its height was almost equal to its breadth (Figs. 12, 34) 

 becomes atterwards semicircular (Fig. 13), later still sickle-shaped (Fig. 14), and shortly before hatching almost 

 straight (Fig. 69). This is caused probably by the peculiar development of segments. All the segments seem to 

 develop most vigorously at the line midway between the ventral and dorsal median lines, i. e., all the segments have 

 their greatest antero-posterior extension on this line, and become shorter and converge, like the frame pieces of a 

 folding fan, toward both the ventral and dorsal median lines. Therefore the external ends of the brain are pushed 

 anteriorly by the growth of the succeeding segments. About two weeks before the hatching of the embryo the brain 

 proper becomes divided into two transverse portions by a constriction (Fig. 69). Thus the brain of Limulus may be 

 divided into four jiarts; the ganglion of the median eyes, the ganglion of the lateral eyes, and the anterior and pf)s- 

 terior portions of the brain proper. These four parts are arranged in three transverse rows. The anterior row is 

 occupied by the two pairs of the optic ganglia, the middle row by the anterior portion of the brain proper, and the 

 posterior row by the posterior portion of the brain proper (Fig. 69). 



We have quoted Kishinouye's observatiou.s at leugth, because they clearly and simply ex])lain 

 as no one had done before, the mode of origin of the ganglia of tlie brain. In Prof. Kingsley's last 

 article little is said upon this subject, his attention not having apparently been directed to the 

 development of the ganglia of the brain. 



My own imperfect observations confirm those of Kishinouye, but were made on a stage appar- 

 ently before that represented by his Fig. 13, and after that of his Fig. 12. The legs in my embryos 

 had not yet become divided at the ends into claws, while there were three pairs of abdominal 

 appendages. It also appears to be of a later stage than that represented by Kingsley in his Fig. ;>2, 

 though the ambulatory or cephalothoracic legs of my embryos seem less advauced in development. 

 In ray embryos also the neuroblasts had disappeared, though I made repeated attempts to dis- 

 cover them. Kishinouye states that " they disappear when the ventral nerve cord is divided into 

 ganglia and begins to be separated from the epiblast" (p. 73). 



King.sley's Fig. 32 well represents the cerebral and lateral-eye lobes ; but his sketch does not 

 give a clear view of the median-eye ganglia, which in my specimens were distinctly separated from 

 the lateral-eye ganglia and the cerebral lobes, and were somewhat conical in shape. I reproduce 

 on PI. XVII, some camera sketches of the lobes of the brain seen in the stage represented by the 

 shaded Fig. 1, the mouth at this time being situated between the first pair of api^eudages. 

 The eggs were taken from the vicarious chorion or deutovuni, and stained from two to three minutes 

 in alcohol cochineal, so as to bring out quite clearly the ventral plate and ijarts of the germ, which 

 had been ft-eshly killed. All the figures oq this plate were made from a single embryo. 



In Fig. 2 the relation of the lobes is shown by a camera sketch made in direct sunlight. The 

 lateral-eye lobes or ganglia are seen to be distinct from the cerebral ganglia {cer. gang.), and in front 

 of the former are the triangular median-eye lobes. I could not detect any traces of a second pair of 

 median-eye lobes or median eyes; and, as already stated, I am led to think that Patten was mis- 

 taken in supi)osing that they exist. Just above the mouth (m) is a shield-shaped or somewhat tri- 

 angular convex area, which is not figured by Kingsley, and of the nature of which I am doubtful, 

 unless it be the rostrum or upper lip. It was seen very distinctly and at different times. In front 

 of it is a small depression (probably the neuropore of Patten), and a larger one is seen in front of 

 the union of the cerebral lobes. 



Fig. 3 is another sketch made from the same egg, showing the same parts from a side view. 

 In this figure there is represented an irregular depression between the second pair of abdominal 

 appendages, which, however, was not always seen. Fig. 3a is a camera sketch of the head of the 

 embryo seen from one side, the left side being the part most distinctly seen. 



The neuromeres were distinctly developed, a pair to each pair of appendages. In the abdomen 

 three pafrs were distinctly seen, as reiiresented in Figs. 4, 5, and 6. I was able to see them very 

 distinctly at different times. In Kingsley's Fig. 32 no abdominal neuromeres are represented. His 

 figure may represent a later stage, though I hardly understand why he does not represent the 

 third pair of abdominal legs, which I repeatedly saw, my Fig. 5 being a carefiil sketch of those 

 of the right side made in dii-ect sunlight. In Fig. 6 the vent or jjroctodfeum was observed, situ- 

 ated between the last two neuiomeres. 



