366 AETflUR WILLBT. 



In B. cultellum, as well as in the Bahama species, the 

 predominance of the right gonads over the left has been accen- 

 tuated to such a degree that the latter have been entirely lost. 

 Whether or not rudiments of the left gonads appear at any 

 time in the development remains to be decided. 



Such instances of unilateral asymmetry as that described 

 above are always of interest, since they are obviously ceno- 

 genetic deviations from the normal, which can in a measure be 

 satisfactorily accounted for. 



Since, according to Boveri's observations, the development 

 of the reproductive organs of Amphioxus takes place after the 

 metamorphosis of the larva, it is evident that the occasional 

 partial asymmetry of the gonads (in respect of size) which I 

 have noted above in the Mediterranean species, and the com- 

 plete asymmetry of the gonads in B. cultellum, &c., must 

 belong to a different order of phenomena from the remarkable 

 asymmetry of the pharynx in the larva of Amphioxus. More- 

 over, Boveri has shown that the perigonadial ccelom is a deri- 

 vative of the myocoele, and the myotomes are not involved in 

 the larval asymmetry. 



It would seem, in fact, that the absence of the antimeres of 

 the right gonadic pouches in the Bahama species and in the 

 Australian species is due to considerations of economy of 

 growth and accommodation to a limited space. Provision 

 being made in the economy of the organism for a certain 

 bulk of gonads, the onus of this can either be shared equally 

 by the two sides, or a greater proportion can be assigned to 

 one side, or finally the entire mass can be confined to one 

 side. It is difficult to give a priori a reason why it shoukl 

 always be the same side which is affected by this unequal 

 growth. 



The above would seem to be the correct mechanical explana- 

 tion of the asymmetry in question, the hypertrophy of the 

 gonads of one side necessarily leading to the final atrophy of 

 those of the other side. Whether it is correlated physiologi- 

 cally with any greater locomotor activity on the part of the 

 species iu which it occurs must remain an open question. 



