18 



THE VENOM OF HELODERMA. 



The lobes are the primary subdivisions of the gland. They vary from 

 three to four in number and are arranged in a longitudinal series. They in- 

 crease in size from front to back. Each lobe is in reality a structurally inde- 

 pendent organ, the different lobes being separated by complete fibrous parti- 

 tions and opening by separate apertures to the exterior; they are bound into a 

 compact whole by the investing fibrous capsule (c/. figs. 1,3, and 4). In form 

 they are roughly club-shaped, their upper excretory portions are narrowed, 

 while their lower, glandular portions are rounded and swollen (figs. 3 and 4). 

 Each lobe is a sac, containing a relatively large central excretory cavity, which 

 narrows at its upper end to form a short excretory canal. This canal opens on 

 the outer side of the jaw close to the base of the tooth. The wall of the sac is 

 of considerable thickness and consists of lobules of glandular tissue. Numer- 

 ous fine tubules, representing the intralobular ducts, open from the lobules 

 into the central cavity. 



The general position and structure of the gland is shown in figs. 1 and 3. 

 It consists of four lobes, directed from above downwards and backwards. 



Fig. 3. Lateral view of head, showing poison gland consisting of four independent sacs. Each sac is cut tangentially, 



showing its central duct or cavity. Natural size. 

 Fig. 4. Enlarged view of same poison gland shown in fig. 3. Slightly diagrammatic. Designed to give a clearer 



view of external openings of poison ducts and their relation to the teeth. Portions of three bristles are 



shown inserted in the last three openings. 



Their upper ends converge close to the anterior border of the lower jaw. This 

 convergence would seem to indicate the formation of a common excretory duct, 

 but, as already mentioned, such a common duct is not formed, each duct open- 

 ing quite independently of the others, as was determined by the use of bristles 

 and the ejection of the secretion under water. In the latter case a thin stream 

 of fluid escaped from each opening. 



As regards the course of the ducts, my observations are in accord with 

 those of Stewart (1891) and opposed to those of Fischer (1882) and Shufeldt 

 (1890). The last two authors described the ducts as originating from the 

 mesial surface of the gland, passing upward through the lower jaw and open- 

 ing within the mouth at the base of the teeth which they supplied. Stewart 

 maintained that "the ducts pass directly from the gland to their openings, 

 which are situated to the outer side of a fold of mucous membrane intervening 

 between the lip and the jaw." Stewart's contention is undoubtedly correct. 

 The so-called ducts of Fischer and Shufeldt are, as Stewart asserts, the 

 branches of the inferior dental nerve which pass out through foramina in the 

 lower jaw and enter the mesial surface of the gland (see fig. 2). 



The statement of Shufeldt that the ducts open at the base of the teeth is 

 not strictly correct. They lie, as Stewart observes, to the outer side of the 



