bulb is absent, only the pin remaining. MR. R. J. BAKER kindly 

 examined these organs for me with a twelfth-inch oil-immersion lens, 

 but was unable to discover any signs of curved bristles surrounding 

 the pin. The measurements of the sensitive organ are : length, 8/u., 

 breadth, 5/u. and length of pin 3/u. 



In the beautiful transparent larva No. 18 already mentioned, the Sensory bulb. 

 sensory organs (see fig. 14), which are highly developed, are undoubtedly 

 of the " bulb " and not the " bow-net " type. The bulbs are not placed 

 opposite each other but alternate on very short stalks, and a new 

 segment seems to have been introduced between them. Each consists 

 of a perfectly transparent smooth bulb enclosing a small basal pin 

 which only extends a short distance into the bulb ; the bulb is four 

 times as large, but the pin is only the same size as in C. pusio. I 

 have only found the bow-net in larvae belonging to the " Pusio " group 

 in species resembling very closely those drawn by DR. LAUTKRBORN 

 in his Fig. n (closed bow-net), in Fig. 13 (open bow-net) and in one 

 which is probably the same as my Larva No. 5. Possibly the curved 

 bristles originated as longitudinal thickenings in a bulb-like organ, 

 while the intermediate spaces became thinner and finally disappeared 

 setting the ribs free. DR. LAUTERBORN has suggested that they may 

 serve the purpose of giving information to the creature of some change 

 in the chemical or physical quality of the water outside the tube, but 

 I am more inclined to give them a tactile function, at any rate in the 

 two species whose habits I have studied, No. 4 and No. 5. I do not 

 think that in either of these species the organ is of much functional 

 importance to the insect, and we have yet to find the larva whose 

 mode of life brings them into full activity. Other examples ot perfect 

 though apparently functionless organs will be mentioned further on. The 

 sensory bulbs in C. pusio, in the stalk-cased larva (No. i), and in the 

 transparent larva (No. 18), are tactile I should think, and in the arm- 

 builders they take the place of eyes in looking for particles on their 

 webs. 



Beyond the clypeus and between the bosses of the antennae lies Labrum. 

 the labrum. This organ in the living larva hangs down as a flap or 

 upper lid in front of the mouth. When the larva is placed under a 



