188 bulletin: museum of comparative zoology. 



later is certainly the chief, if not the only, excretory organ of the body, 

 must be functional and functional in the way of its later activities. I 

 therefoi'e believe that the antennal gland in the first larva is a functional 

 excretory organ. 



(b.) In Older Larvae. 



The antennal gland in the second larva shows no marked difference 

 from that in the first, either in shape or in histology. There is, how- 

 ever, as compared with the first larva (see page 184), a difference in size, 

 which again taking averages, is now : 



Maximum proximo-distal axis, 0.3 mm. 

 " dorso-ventral axis, 0.3 " 

 " latero-median axis, 0.25 " 



If we assume, in view of the simplicity of the organ at these stages, 

 that its secreting surface is about equal to the surface of a parallelopipedon 

 having the dimensions of the whole organ, we find that the area of the 

 secreting surface in the second larva is 40-50 per cent greater than in the 

 first. The average length of the second larva (see Herrick '95, Table 34) 

 is only about 13 per cent more than that of the first. If we compare the 

 cubes of these dimensions we get an increase of something over 40 per 

 cent in the bulk of the larva ; consequently the increase of secreting 

 surface in the antennal gland simply about keeps pace with the increase 

 in bulk of the larva. 



In the third larva we get the beginning of that process of complication 

 by which the antennal gland of the adult animal is developed from the 

 relatively simple organ of the time of hatching. Between the conditions 

 in the first and second larvas there is only the difference of size. Be- 

 tween the conditions of the second and third larvae there is a difference 

 due to increase in size, by reason of which the gland comes to lie largely 

 in the body instead of in the appendage only, and in addition a differ- 

 ence resulting from the development of long slender evaginations on 

 the dorsal and median faces of the ectodermic sac. These evaginations 

 have only a very small lumen, but the lumen is always in connection with 

 the main cavity of the ectodermic sac, as is shown in Figure 50 (Plate 

 6, evacf.). By such evaginations the secreting surface is greatly increased 

 without a correspondingly large demand for space in the body cavity. 



In the third larva there also begin to appear at the free ends of the 

 cells composing the wall of the ectodermic sac the peculiar globular 

 vesicles which form so marked a feature of the adult gland. They are 

 less well marked and less abundant here thau in the older larvse. 



