312 INEZ WHIPPLE WILDER. 



which is, however, thin in the region immediately surrounding 

 the gland. Embedded thus in the loose vascular corium, each 

 gland comes to be surrounded by a capillary ring (cap), which, 

 joining similar rings about the neighboring glands, forms a part 

 of the rich capillary network of the skin. These glands and 

 their ducts, the latter slender and lined with thin cells which are 

 continuous with the cells of the external layer, are fully formed 

 at the time of metamorphosis and before the first moult (ml, 

 Plate VI., 31) occurs. The nature and function of their secretion 

 and the methods by which they are replaced must be left for 

 further and more extended investigation. Suffice it to say that 

 many, if not all of them, show from the first a striking similarity 

 in structure to the relatively larger and less numerous acinous 

 larval glands above described. One anatomical distinction 

 between the larval and adult glands must, however, be clearly 

 understood, namely, that the larval glands lie wholly below the 

 level of the dense corium, the ducts alone passing through this 

 to reach the external surface. The larval glands remain func- 

 tional up to the time of metamorphosis, and thus in the meta- 

 morphosing larva both the larval and the adult sets of glands are 

 present, the former beneath the dense corium, the latter external 

 to it within the loose corium (cf. Fig. 15, e). After metamor- 

 phosis, however, the larval glands collapse and lose their con- 

 nection with the external surface, their cells undergo atrophy, 

 and the glands rapidly disappear. It is this atrophy of the 

 supra-branchial group of glands which results in the marked nar- 

 rowing of this region of the head at metamorphosis (cf. Fig. 17). 

 The naso-labial glands consist of a series of tubular glands 

 opening in close proximity to the external nasal orifices and along 

 the border of the naso-labial groove (Whipple, '06). Of these 

 glands (many of which become very extensive in the fully 

 developed adults) the two largest (nli and nh, Figs. 18, 19, and 

 20) begin their development before metamorphosis, and at the 

 time of metamorphosis have attained a size and condition indica- 

 tive of their functional importance in adult life. The one of 

 these which opens at the dorsal angle of the nasal orifice extends, 

 at this time, beneath the skin as far posteriorly as the anterior 

 angle of the orbit, is somewhat convoluted, and branches near 



