TROCHOPHORK OF HYDROIDES UXCINATUS (eLTPOMATI's) . 563 



Apart from the Serpiilids, the development oE Thalas- 

 sema, Podarke, and Polygordius closely resembles that 

 of Eupomatus in its essential features. The cleavage in 

 these is of the equal spiral type of that of Eupomatus, and, 

 in fact, the early cleavage of Podarke, Thalassema, and 

 Eupomatus are almost similar cell for cell until the time of 

 gastrulatiou. In each the gastrula is formed by invagina- 

 tion, and a well marked blastoccelic cavity is present. In the 

 later stages of gastrulatiou Thalassema and Polygordius 

 more closely approach Eupomatus than does Podarke. 

 This is possibly due to the fact that the trochophore of 

 I*odarke is somewhat modified, apparently not having any 

 head-kidney. Polygordius, with its large blastopore, 

 represents possibly a more primitive condition than do 

 the others. Thalassema in the pre-trochophoral stage 

 approaches nearer Eupomatus than do the others, for in 

 Polygordius the head-kidneys form some time before the 

 mesoderm bands. Tlie details of the resemblance between 

 these four will be considered further on. 



o. Matekial and Methods. 



When the sexual products are ripe in Eupomatus it is an 

 easv matter to distinguish the sexes from the colour of the 

 body. The female is bright yellow, while the male is white. 

 In Naples they grow in dense colonies attached to stones, 

 the sexes being evenly proportioned, although the males and 

 females show a slight tendency to occur together in separate 

 spots in the colony. Their tubes stand upright, being attached 

 by one end. 



In ettectiug fertilisation under artificial means, it is 

 unnecessary to wait until the eggs are deposited as in man}' 

 Annelids, as Nereis, Podarke, Phyllodoce. The ripe 

 eggs cut from the body-cavity fertilise as readily as those 

 laid iu the normal manner. 



The egg of the Neapolitan Eupomatus seems to be more 

 opaque than that studied by Hatschek at Trieste, for I have 



