REMARKS ON THE DEVELOPMENT OF AMPHIOXUS. 363 



has been figured by me in fig. 9 of my paper, and it is clearly 

 seen that the " clear space " referred to by Samassa is in the 

 ventral lip. Since, further, I have figured a much more 

 complete set of intermediate stages of the gastrulation than 

 Samassa, I must hold to the opinion that in this point an 

 error has been made by that investigator. 



As to the mesoderm, Samassa's observations are obviously 

 incomplete, no mention is made of the head cavities, and the 

 whole subject seems to have interested him less than the 

 subjects of the segmentation and gastrulation. None of his 

 statements, however, are irreconcilable with my position. 



Legros' paper (5) is unfortunately only known to me 

 through the abstract of it given by Klaatsch in the ' Zoolo- 

 gisches Centralblatt,' but the results therein communicated 

 have awakened the utmost astonishment in me, and prove con- 

 clusively not only that Legros has never seen the earlier stages 

 in the development of Amphioxus, but also that he has never 

 had properly preserved larvse at all. I may pass over his 

 theoretical conclusions in silence, for any conclusions founded 

 on such erroneous observations are devoid of any value. 



Legros states that the pre-oral pit of the larva is an ecto- 

 dermal ingrowth, and denies that the club-shaped gland has 

 an outer opening. It will be remembered that the accepted 

 view of the origin of the pre-oral pit referred it to the left 

 head cavity of the embryo. Now I must reiterate this view 

 in the strongest possible terms. I have seen the pre-oral pit 

 in the larva about the time of the formation of the mouth as 

 a closed vesicle, not once or twice, but twenty to thirty times, 

 — as often, in fact, as I examined a larva of that age. I have 

 further traced it back until I found it arising as a thickening 

 of the left side of the head cavity. As to the club-shaped 

 gland I am entirely of Willey's opinion that it is a gill slit. 

 I have seen its origin again and again as a pouch of the 

 pharynx, and I have also found its external opening, but to 

 see this it is necessai'y to have larvse preserved in osmic acid. 



I have only mentioned the club-shaped gland incidentally 

 in my former paper, for it never occurred to me that the 



