•220 Sfwh'es in tlw PlojHkohHpi of Fertilization 



a miiiutu, when this mass of eggs and sperm lying at the apertures of 

 the genital ducts has reached a certain size, it is suddenly expelled 

 into the water through the exhalent siphon by a violent contraction 

 of the muscles in the body wall. The process is then repeated. The 

 whole period of egg and spei-m deposititm usually lasts fVom five to ten 

 minutes. 



Castle (1) first observed that Ciona intestinalis deposits its genital 

 products at a definite time of day. His animals always discharged 

 their eggs and sperm an hour or an hour and a half before sunrise. 

 Morgan (9) states that at Woods Hole " the eggs are laid in the early 

 morning, at dawn." Seeliger (14), however, remarks that at Trieste 

 there is no such regularity in the time of deposition. With the Ciona 

 at Naples, 131 depositions of genital products were observed by me 

 in a number of isolated animals during the months of December and 

 January. 105 of these took place in the late afternoon after 5 o'clock, 

 that is to say after dusk had set in. Six depositions were in the night 

 (as judged by the state of segmentation of the eggs on the following 

 morning), and 20 in the early morning, about sunrise. Almost all the 

 early morning depositions were by individuals which had been laying 

 regidarly for a number of days in the late afternoons, which suggested 

 that morning laying was an effect of the laboratory conditions. As 

 this was not an invariable rule, it is hardly of value to publish the 

 exact i-ecords. The only conclusion to be drawn is that in the great 

 majority of cases eggs and sperm were discharged in the late afternoons, 

 and that in no cases did the depositions occur during the period of 

 bright daylight. It is hoped to decide whether the stimulus to dis- 

 charge the genital products may be given by a change from light to 

 darkness, or from darkness to light, by further laboratory experiments, 

 which will also deal with the mechanism of ejection. 



The present investigation was carried out at Naples between 

 December 1912 and July 1913, while I was occupying the Cambridge 

 University Table. I would like to take the opportunity of tendering 

 my very best thanks to the Staff of the Zoological Station, both for 

 the valuable advice and help afforded me throughout the course of the 

 work, and for the trouble taken to procure an abundant supply of 

 material, which was brought in fresh from the sea almost every day. 

 My thanks are also due to Mr R. H. Comf)ton of Uonville and Caius 

 College, Cambridge, who originally suggested to me ;ui investigation 

 of the problem of self-sterility. 



