14 



species have this power somewhat more developed, and this is interesting 

 as it shows how the completely retractile antennae of Tanypus (a closely 

 related genus) may have originated from small beginnings. From the 

 distal end arises a second segment, broad at the free end but narrow 

 at the base ; beside this on the ventral side arises a double transparent 

 hair the longer branch equalling the second segment in length. At the 

 distal end of the second segment, arising from a transparent enlargement, 

 are three processes, a median process consisting of three minute 

 segments, and two transparent processes of the same length swelling 

 out into minute transparent bulbs. There is also a small papilla between 

 the outer and central processes. 



There seems at first sight a great difference between this specialized 

 antenna of C. pusio and the rudimentary antennae of the blood-worms, 

 but the homologous parts are easily identified. In the blood-worm 

 there is a stout basal segment with sensory spot, equivalent to that of 

 C. pusio ; beyond this are two terminal pieces, the one simple and the 

 other composed of three or four joints, the simple piece is equivalent 

 to the double hair of C. pusio, while the proximal piece of the four- 

 jointed member represents its second segment ; finally the three last 

 joints are easily identified with the three-jointed median process, which 

 is comparable in size. 



The lateral processes with their transparent bulbs have no 

 representatives in the blood-worm, but among the smaller free-swimming 

 species they can generally be detected. This fact points to the 

 conclusion that the now rare and specialized form of antennae was 

 probably possessed by the ancestral form from which most existing 

 species have diverged in a degeneratory manner, and this ancestral form 

 would also have probably possessed the i3th segment already referred to. 



Bow.net. This form of antennae was first described by DR. LAUTERBORN and 



figures were given of various species showing the curious form of sense 

 organ borne by the lateral processes. This organ (see fig. 15) he calls 

 a " bow-net " (Reuse). In C. pusio larvae the " bow-net " is exceedingly 

 small if it exists at all ; it appears rather to be a minute transparent 

 "bulb" surrounding a small sensitive "pin," and sometimes even the 



