REPORT ON A COLLECTION OF AMPHIOXUS. 367 



According to Andrews the Bahama species " swims free in the 

 evening, both at Bimini and in Nassau Harbour." 



There is thus every reason to suppose that the above- 

 described unilateral asymmetry of the gonads in certain species 

 of Amphioxus belongs, broadly speaking, to the same category 

 as, for example, the well-known asymmetry of the female 

 genital glands and the lungs of snakes, in which the respective 

 organs of the right side usually predominate over their anti- 

 meres on the left side, the latter being often rudimentary; and, 

 again, the female reproductive organs of birds, in which the 

 left ovary and oviduct predominate over the right, the latter 

 being either absent or rudimentary. 



There are seventeen to twenty unpaired gonadic pouches in 

 B. cultellum. When there are as many as twenty the 

 first one lies at the base of the 9-lOth myotome. In one 

 specimen, taken from a bottle labelled " Mabinag, Oct. 24th, 

 1888," there were quantities of free ova in the atrial chamber 

 derived from the discharge of the anterior eight or nine gonadic 

 pouches, while the nine posterior pouches still remained intact. 

 Another specimen, in which the hypertrophy of the unilateral 

 gonads was carried to an extraordinary pitch, was taken on 

 Dec. 24th, 1888. 



This, therefore, may be taken to indicate the time of spawn- 

 ing of B. cultellum, which is somewhat later than is the case 

 with the Mediterranean species. In fact, it would appear as 

 though the spawning of B. cultellum commences at about 

 the time of the year at which that of B. lanceolatura 

 ceases. 



I am not aware of any observations on the habits of B. cul- 

 tellum, but the special elaboration of the dorsal fin would 

 seem to point to the fact of its being, like the Bahama species, 

 an active swimmer. 



As for the significance to be attached to the continuity of 

 the right metapleur with the mesial ridge of the ventral fin, it 

 seems to show that the metapleural folds or ridges are, after all, 

 structures of the same nature as the median longitudinal 

 ridges which constitute the fins of Amphioxus. If the meta- 



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