352 



C. FORSTER COOPER. 



ran up side by side, and there was only one division of the coelom as figured. According 



to Benham this is a fairly common variation in Amphioxus 

 lanceolatus'^. 



The alimentary canal from the region of the atriopore 

 stretches through 21 myotomes to the anus. The liver caecum 

 is comparatively short, nmning through only nine myotomes. 



The excretory organs are of the usual type. The epithelial 

 patches on the floor of the atrium are numerous and well- 

 marked. Nephridia on the gills could also as a rule be seen. 

 They have the usual structure as described by Goodrich °, and 

 their atrial openings were distinctly observed. Lankester's brown 

 furmels do not occur. 



The circulatory and nervous systems both conform to the 

 usual type, but in the latter no olfactory pit was found. Only 

 the gross anatomy of these organs could be made out, but as 

 far as the histology was observed, there is no difference between 

 them and the same organs described for A. lanceolatus. 



Since working out this form I have received a large number 

 of specimens of H. maldivense from Mr Crossland, who obtained 

 them at Zanzibar. I have been thus enabled to make a fuller 

 list of measurements, which shew that the size of the animal 

 may be larger than the Maldivan specimens led me to expect, 

 although the average remains about the same. These measure- 

 ments will be found in Table II. p. 363 of Mr Punnett's 

 "Note on Meristic Variation in the Group." Unfortunately the 

 specimens were not very well preserved. The gonads had in some cases broken away, and 

 in others, marked with a note of interrogation (?), their position was a 

 little doubtful. 



To sum up the specific differences between this form and H. bassa- 

 num. The myotome formula is on average 73 in all, 45 from the head to 

 the atriopore, 16 from the atriopore to the anus, and 12 from the anus 

 to the tail ; while the total number in H. hassanum is nearly the same, 

 i.e. 75, there is a constant difference of two myotomes in the caudal region, 

 H. hassanum having 14. The dorsal fin is much deeper than in hassanum, 

 the rostral fin is a little smaller and the notch is very much less marked. 

 The preoral cirri number 23 as against 33, and the ventral fin is without 

 the paired fin rays and spaces'. 



3. BRANCHIOSTOMUM PELAGICUM. 



Fig. 80. Heteropleuron maldivense ^ 

 Section just io front of the velum. 

 The origin of the buccal cirri is 

 seen at the bottom. 



Fig. 81. Heteropleuron 

 maldivense. Abnormal 

 double gill bar. 



Through the kindness of Mr J. J. Lister I have been enabled to 



examine a specimen of an Amphioxus, which was obtained by him in 

 the year 1888 in latitude 21° 16' S. and longitude 80° 50' E. i.e. in the 



^ Quart. Joum. Mic. Sci. 1893, vol. xxxv. Part 1. Kirkaldy {loc. cit.), however, avows that her specimens were 



" Quart. Joum. Mic. Sci. 1900, vol. xviii. Part 4. in good condition, so that a mistake could hardly have been 



' Dr Benham {Q. J. M. S. vol. xliv. p. 276) states that made. Variation in this respect may occur, 

 double fin rays do not occur in the ventral fin of H. hassanum. 



