AN UNDESCRIBED ACRANIATE. 231 



pigment in a few, very thin, sections immediately posterior to the 

 extreme tip of the ventricle, Fig. 7. 



As far as could be observed in surface views of both living and 

 preserved specimens and in transverse and longitudinal sections of 

 both young and adults no anterior neuropore or " nasal pit" exists, 

 nor any such connection of the anterior part of the brain with the 

 epidermis. 



The pigment spots of the neural tube are very conspicuous in 

 life and in sections as large cap-shaped masses about individual 

 ganglion cells of the ventral part of the cord near the base of the 

 median fissure or canal. 



The spots begin a short distance posterior to the brain and soon 

 become more crowded to form a series, on each side, that ends pos- 

 teriorly before the caudal process is reached. There is throughout 

 a disposition to aggregation in linear groups suggesting a meta- 

 meric arrangement, but the short lines of pigment spots are not 

 actually arranged with reference to the myo tomes. 



This pigment is very resistant, as attempts to remove it in 

 Grenacher's depigmenting liquid were not successful after many 

 days' immersion. 



In summarizing the above account of the Bahama amphioxus, 

 we find thdt its peculiar structures, asymmetry of the reproductive 

 organs and great extension of the tail fin, do not throw light upon 

 the morphology of the acraniates, but are such characters as may 

 be explained as secondary departures from a type more like the 

 common European form. Thus the lack of the left gonads is no 

 doubt a loss of what was at one time present. The extension of 

 the tail is also a secondary feature ; for we will see later that the 

 actual number of myotomes has not been decreased, on the con- 

 trary there are 66 here as compared with 61 in the European 

 lancelet, so that we have no ground for supposing that the caudal 

 process was once accompanied by myotomes. It is rather a pos- 

 terior outgrowth of use in swimming, a true caudal process. Yet 

 the presence of the neural tube in this non-muscular region does 

 suggest the former existence of muscles; on the other hand the 

 extension of the brain beyond the anterior myotomes (Fig. 10) 

 furnishes evidence as to the possibility of nerve tube and notochord 

 extending out together into new terminal structures. 



