230 E. A. ANDREWS. 



fibers in each sub-atrial ridge before they unite ; there is thus a 

 double series of transverse fibers that subsequently unite with one 

 another across the middle line. In each half of the series, on the 

 right and on the left, the fibers have the peculiar grouping seen in 

 Figure 16. There are three or four groups for each myotome, each 

 group being due to a special centre of growth about which the 

 fibers are arranged in pairs and become gradually longer as they 

 adjoin the other groups. Eventually all the fibers seem to become 

 of equal length so that this segmentation is obliterated. 



The agreement of the groups upon opposite sides of the median 

 line is also noticeable as a marked case of bilateral symmetry in 

 the arrangement of individual cells upon disconnected, opposite 

 sides of the body. 



No thorough examination of the nervous system was attempted, 

 but it seems to present no marked difference from the state of things 

 found in the common amphioxus. There are dorsal and ventral 

 nerves and amongst the former a large one, seen in Fig. 10, that 

 arises from the posterior part of the brain, branches freely and is 

 distributed to the anterior part of the median fin where there seem 

 to be terminal organs in the living specimen. Two slender nerves 

 continued from the anterior end of the brain, along the notochord 

 are sometimes seen to have a hollowed out b?e which may be an 

 indication of what Ayres(34) has described as optic diverticula or 

 lobes in the common lancelet, which, however, seem here to be rather 

 the results of distortion in preparation than normal conditions. 



The ventricle of the brain has in longitudinal median section 

 very much the form and proportion represented by Kiipffer(33), 

 Figs. 21-22, but the posterior ventral diverticulum could not be 

 recognized as a cavity though indicated by a non-nucleated, 

 clearer region. 



In transverse sections we have successively the appearances seen 

 in Figs. 7, 8, 9, which represent the ventricle at its anterior, middle 

 and posterior portions with the relative size of lumen and wall. 



The pigment spot at the anterior end of the brain presents nothing 

 to suggest that it is in any sense an eye. It is not placed exactly 

 as in the above figures of Kiipffer but forms a terminal cap-shaped 

 deposit in the conical tip of the brain, is a collection of pigment 

 in the conical tip of the ventricle wall and is thus cut as a ring of 



