558 John Beard 



ment and arrangement of muscle eells around the stomodaeum. The 

 stomach (fig. 21, 24) is large and well marked off from the stomodaeum 

 and short intestine. 



In some larvae the primitive two pairs of setae are the only ones 

 developed, and exist stili at the fifth or sixth day, having only inereased 

 in length. In most cases however additional setae are formed, and 

 the larva of five days very often has free pairs of long setae, which 

 usually equal the length of the larva itself and very often exceed it 

 (fig. 21, 22). The anal papilla is uow well developed and retraetile. 

 The anus stili opens on the dorsal side of it (figs. 22 and 23) . Two 

 sections of five days larvae are given in figs. 27 and 28. In them it is 

 easy to recognise the larvai nervous thickening of the praeoral lobe and 

 the muscles and sacs of the setae {se.s). Biit they also show another 

 point. This is that certain of the mesoblast eells remain in an embry- 

 onic state as two bands, and are not functional in the larva. These eells 

 [me.r] first take on a renewed activity on the later stages, and form in 

 part or entirely the musculature of the permanent feet. We shall have 

 occasion to refer to these later on. 



In aquaria placed in the working room of the zoologieal station of 

 Naples the period of free larvai life appears to last for seven or eight 

 days. This is of course at the relatively high temperature, compared 

 with that of the sea, obtaining there. Whether it be of longer duration 

 in the naturai state at the sea bottom is not determinable. The larvae 

 appear to be exclusively bottom forms. They swim and creep about the 

 bottom in search of food. This fact coupled with their minute size, 

 never more than 0,08 mm in length, accounts for their not having been 

 previously observed. Small as they are they eould hardly have escaped 

 Observation had they been surface forms. They are somewhat sluggish 

 creatures and do not move about very much. When they do move it 

 appears to be sometimes by the aid of their setae, sometimes by the aid 

 of their cilia. 



Thii'd period of larvai liistory. 



The larva described in the preceding pages attains its full develop- 

 ment as a larvai form when about four days old. When about seven 

 days old its characters begin to alter. Already in fig. 24 the setae are 

 partially cast off. 



It is now preparing to take up its adult habitus on a Comatula. To 

 this end the provisionai setae are cast aside (fig. 23Ì and the larva 

 moves about with a worm-like motion, reminding one very much, if the 



