THE DEVELOPMENT OF OPHIOTHEIX FRAGILIS. 569 



tliem alive more than eight or niue days. The second female 

 was placed in a half-gallon jar along with two males and 

 spawned in a natural manner. The larvre were exceedingly 

 vigorous and developed with great rapidity; they differed in 

 a marked manner from the result of previous cultures so far 

 as the earliest stages were concerned. I was able to rear 

 them for sixteen dayS; by which time the hydi-ocoole had made 

 its appearance. Their eventual death was clearly due to starva- 

 tion, as the Phytoplankton was extraordinarily scanty in that 

 year. Reviewing the account just given, it will be seen that 

 in 1898 a culture was obtained as the result of artificial 

 fertilisation in which some larvse completed the entire de- 

 velopment, until the end of metamorphosis. In 1899 and 1905 

 similar cultures gave larva3 which were only able to carry on 

 the development for about a week; whilst in 1905 a culture 

 obtained by what may be termed natural fertilisation gave 

 larva3 which grew and developed vigorously as long as food 

 was available, and which in their earlier stages were different 

 from those which resulted from artificial fertilisation. The 

 main mass of the material was obtained from Plankton. If 

 we take the successful culture of 1898 as giving an indication 

 of the time required to effect complete development, it will 

 follow that metamorphosis is finished in about a month, and 

 the approximate time for the appearance of other organs is 

 given in the following table : 



Free-swimming blastula .... 24 hours. 



Gastrula ....... 36 „ 



Formation of coelom . . . . 2 days. 



Stomoda3um joins gut .... 3 „ 



First transverse division of coelom . . 8 „ 



Formation of hydrocceles . . . 16 „ 



Left hydrocoele five-lobed ... 20 „ 

 Encircling of oesophagus by hydrocoile . 23 ,, 



Absorption of larval arms complete . 26 „ 

 These times, however, are only approximate, and the rate 

 of development varies very much with the amount of food 

 present, and possibly from other causes too. In particular 



