184 ARTHUR WILLEY. 



transitional forms, which were carefully drawn and described as 

 observed in the living condition. These observations form the 

 substance of the present memoir. I may possibly find it desir- 

 able to add to this hereafter an account of some of the struc- 

 tures involved, as determined by means of sections. For this 

 determination I have an ample supply of preserved material. 



Habits of the Larv^. 



The conditions under which the material was obtained last 

 year differed in a curious way from those of the preceding year. 

 In 1889 the larvse of Amphioxus were present in the lake at Faro 

 in great numbers, especially during the months of July and 

 August ; while last year, during the same months, they were 

 comparatively rare, and their place seemed to have been taken 

 by an incredible host of Doliola of the first or larval generation. 



Exactly in what way the presence of vast numbers of 

 Doliola affected the larvse of Amphioxus I was not able to 

 make out, because the spawning of Amphioxus was prolific in 

 the extreme. Possibly the breeding of Amphioxus as a 

 whole commenced rather earlier last year, and the larvae may 

 have taken to the sand mainly before July. I found numerous 

 Doliola with ova and gastrulse of Sagitta in their pharynx, some- 

 times as many as nine ova in one Doliolum. This might lead 

 to the death of the embryos in question, as it appears to cause 

 the death of the Doliolum. I did not, however, find the ova of 

 Amphioxus in this position, or possibly only in one or two doubt- 

 ful cases. At all events, the scarcity of the larvse of Amphioxus 

 at this particular time of the year was evidently in correlation 

 with the great predominance of Doliolum. 



Professor Kleinenberg informed me of an analogous fact, 

 namely, that Salpse are sometimes very numerous in the harbour 

 of Messina, to the exclusion of other small pelagic organisms. 



When placed in glasses containing fairly clean water the 

 healthy larvae of Amphioxus are seen to be suspended, appa- 

 rently motionless in the water, in a highly characteristic 

 vertical position. The suspension is no doubt effected by the 

 movement of the long cilia with which the epidermis is provided. 



