THE GONOPHORES OP DISTIOHOPORA AND ALLOPORA. 387 



its sharp outlinej and remarkable changes occur in the shape 

 and arrangement of the yolk-globules. My observations are 

 not yet complete of the early stages of the development^ but I 

 hope to be able to publish shortly a separate memoir^ giving 

 a full account of the development of this form up to the stage 

 when the larva escapes from the ampulla. 



During the early stages of development the trophodisc 

 rapidly atrophies, and by the time a layer of columnar epiblast- 

 cells has formed round the embryo no recognisable trace of it 

 can be seen (figs. 22 and 25). 



In the meantime young eggs are migrating from the sub- 

 jacent canals to the base of the ampulla, and in many cases 

 before the larva has escaped a new egg, borne by a new 

 trophodisc, occupies a considerable space in the same ampulla 

 (fig. 25). 



The young eggs (fig. 22, ov.) are frequently seen quite deeply 

 situated in the canal system; those that are nearer to the 

 ampullae are larger in size and amoeboid in shape. As soon as 

 they reach the ampulla they show very minute yolk-granules, 

 which increase in size with the growth of the egg and the 

 development of the trophodisc. 



The female gonophores of a few species of Stylasteridse have 

 already been figured and described by Moseley (10). 



In Pliobothrus symmetricus ''the gonophores are con- 

 tained in ampullse which are often sunk deep in the coenosteum. 

 .... The ova are solitary, one only being developed in each 

 growing ampulla. Each ovum is developed within the cup of 

 a cup-shaped spadix," i. e. trophodisc. " As the ovum ad- 

 vances in development and increases in size the spadix enlarges 

 with it. Subsequently, however, in later stages, the spadix 

 appears not to increase further, and when in relation with a 

 nearly fully developed planula appears proportionately small." 



In Errina labiata "the female gonophores are closely 

 similar in structure to those of Pliobothrus symmetricus ; 

 but there is this great difference, that whilst in Pliobothrus 

 the ampullae and their contained ova and planulae remain 

 until maturity immersed in the coenosteum beneath its surface. 



