206 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



straight portions, which extend to the frontal margin (fig. 34). The 

 total length is considerably more than the entire length of the larva; 

 as a duct such an increase in length would be difficult to explain; as an 

 attachment filament it explains itself. 



As already stated, the increase in length takes place at the proximal 

 end where the filament is brought in contact with the glandular sub- 

 stance by means of the peg. This peg is slightly different in color 

 and structure from the rest of the filament, and stains differently. 

 At the point where it actually joins the gland it spreads out into a 

 sort of funnel, whose walls are extremely thin and delicate (fig. 13). 

 The walls evidently form a viscid film on the outside of the secreted 

 substance, plastic enough at the proximal end to be pushed along 

 gradually by the accumulating secretion, but rapidly growing thicker 

 and firmer distally. The new film constantly forming at the point of 

 union thus becomes continuous with that which has preceded it, and 

 in this manner the entire organ is formed. 



Nordmann mistook the ends of the filament for the eyes of the 

 larva, while he supposed the coiled portion to be connected with the 

 mouth-parts. But he makes the following pertinent statement : 



The length of the filament (Rohre) is in direct relation with the development and 

 size of the embryo. The longer it is, so much the farther has the development of the 

 animal progressed; the shorter it is, so much the younger is the embryo. 



This is exactly true of the present species, and the fact that this 

 filament is completely developed before the larva escapes from the 

 egg indicates that it is to be used at once. 



Hatching. — The larva is now ready for hatching. This process in 

 the present species is similar to that which has been well described by 

 Claus for Achtheres percarum. The thick wall of the egg sack is so 

 constituted that it becomes weak and brittle through the action of 

 the water at just the time when the larvse have completed their 

 development and are trying their muscles. Through both of these 

 influences, as well as by osmosis, the sack bursts open at one or more 

 places and the larvae pass out into the water. They are still sur- 

 rounded by the various membranes that have been formed during 

 their development, but these are quickly and easily gotten rid of. 



As soon as the water strikes the egg membrane, which it will be 

 remembered is formed of the same cement substance as the external 

 sack, it SAvells a little and bursts from the osmotic pressure. The inner 

 membranes are very thin and delicate, and are easily ruptured by the 

 struggles of the larva, which are increased when subjected to the 

 change of environment. In this way it comes about that the molting 

 of the nauplius cuticle is simultaneous with the escape from the egg, 

 or follows it after an interval of only a few moments. 



With reference to the actual period of hatching, Nordmann stated 

 that the larva3 of Achtheres percarum hatch directly into the first 



