514 Howard Edwin Eiiders-. 



The ''terminal papilla" is an organ for attachment of the larva 

 which, up to this time, has been pelagic. An individual two days 

 older, which, when placed in water in a watch-glass, swam actively 

 for several minutes, became attached by the free end of its ''terminal 

 papilla" to the bottom of the dish. With this point of attachment 

 as a center the larva was seen to swing about in a circle or bend back 

 and forth or from side to side, much as an attached Stentor does. 

 After several minutes I saw the process released and contracted sud- 

 denly. Some individuals swam about trailing it in an extended con- 

 dition as figured by Wilson (Fig. 7, PL 2), others used it more or 

 less to aid as a prop in performing creeping movements on the bot^ 

 tom of the dish. I was unable to rear larvae beyond this stage iu 

 the dishes, but by means of the characters which they possessed I 

 was able to know the larvae in the tow. The following stages are 

 from material taken in the tow. 



Beginning of the Transformation. 



A Chsetopterus larva 1,5 mm. long (Fig. 10) is the youngest taken 

 in the tow net. It possesses three pairs of eye-spots and two incom- 

 plete rings of powerful cilia directly back of the middle of the body, 

 but the apical tuft and lateral flagella are completely atrophied. 

 The beginning of the transformation is accompanied by a change 

 of habit. The larvae swim slowly near the bottom of the dish instead 

 of actively near the surface of the water, as is done by the younger 

 ones. 



The body of the larva in this stage is fusiform and bears mark- 

 ings on its surface that indicate corresponding regions in the adult. 

 For this reason it wall be convenient to refer to the regions as ante- 

 rior, middle and posterior. The anterior region extends backward to 

 the second (in point of development) ciliary ring, w^hile the middle 

 region includes the two ciliary rings together with nearly all of the 

 remainder of the larva ; the posterior region is quite small and incon- 

 spicuous at this time. The middle region is the first to become annul- 

 ated in Chaetopterus as it does in the very similar lan-ae of the 

 closely related genus, 8 plocluetopterus , which were more abundant 

 than Cha?topterus in the towings made in August (1905). 



