Einiges über Halodactylus diaphanus Farro. 515 



cimen (PL XXV, Fig. 4). The smaller cells are triangulär, 

 and the animal forms a mere spot in its centre. As they grow 

 they tbrust aside the surroundiug cells, and the number of their 

 sides increases until they acquire the irregulär hexagonal form 

 of a adult. In the oblique position of the cells (in which they 

 look like a new growth encrusting the old mass like a Flustra) 

 the young cells are less augular, and arranged more regularly 

 at the spreadiug edge (Fig. 5). 



This species afforded an opportunity of examining also the 

 reproductive gemraules. These are readily seen in spring as 

 minute whitish points just below the surface of the mass (Fig. 

 3 aa). Sometimes they are of a darker colour, and exceedingly 

 uumerous, appearing to occupy almost the whole substance. If 

 one of these points be carefully turned out "with a needle it 

 is found to consist of a transparent sac (Fig. 20 a), in which 

 are contained generally from four to six of the gemmules, which, 

 as soon as the sac is torn, escape and swim about with the 

 greatest activity, affording a most interesting subject for mi- 

 croscopic investigation. 



"When viewed with a power of forty, linear measure, they 

 ■ are seen to be of an oval or rounded form (Fig. 20 b and c), 

 convex above, and nearly plane below, and fringed at the margin 

 with a Single row of cilia, which appear to vibrate in succes- 

 sion round the whole circumference. Under an amplification 

 of 120 they assume a different aspect (Fig. 21 and 22), and 

 their minute structure is clearly discerned. Yiewed as opake 

 objects, both the body and cilia have a silvery whiteness, but 

 by transmitted light the former appears of a dark brown, and 

 the cilia of a golden yellow colour. üpon the most convex 

 part of the body, which is not generally in the centre, but 

 leaning to one side, are set from three to five prominent trans- 

 parent bosses surrouuded by a circle; and other circles are 

 Seen extending to the base of the body, the extreme margin 

 of which is bounded by a row of prominent tubercles. These 

 marginal tubercles are from thirty to forty in number, and from 

 the circumstance of the cilia arising from them, it is probable 

 that they are for the purpose of governing their motions, and 



33* 



