36 



tubular glands and the other as the globular or acinose 

 glands. 



The tubular glands (Plate YI., figs. 63 and 65) are 

 situated very near to the salivary glands in the hinder 

 region of the head. Both the secretory and conducting 

 portions of these glands are tubular in structure, and are 

 inter-cellular throughout their course. The distinction 

 between the two portions is very slight ; in the glandular 

 part the cells and their nuclei are rather larger than those 

 of the duct. The ducts of opposite sides pass downwards 

 and forwards close under the hypodermis of the ventral 

 region of the head and, approximating towards one 

 another, eventually open into a common chamber (fig. 

 64). From the latter a short duct passes downwards 

 in an oblique direction, and opens on to the exterior on 

 the ventral surface of the head at the commencement of 

 the ventral groove. The walls of the common chamber 

 are invested with a layer of circular muscle fibres, which 

 evidently have the power of controlling the flow of the 

 secretion into the ventral groove. These fibres resemble 

 in their structure those of the fore-gut, and consist 

 (fig. 64) of a layer of sarcoplasm on the outside with the 

 muscle substance lying wholly internal to it. 



The globular or acinose glands (figs. 65 and 66) are 

 situated in the anterior region of the head, and close to 

 the hypodermis on either side. They each consist of a 

 group of cells, which are similar in structure to those of 

 the salivary glands, and from them a fine duct passes 

 forward and opens into the common canal or chamber in 

 front of the ducts of the tubular glands. 



The ventral groove (Plate I., fig. 3, v.g.) arises close 

 behind the suture {sut. in fig. 12) of the labium, and passes 

 backwards in the median ventral line until it reaches the 

 anterior aspect of the ventral tube, where it terminates 



