THE CALCIFEROUS GLANDS OF EARTHWORMS. 
481 
The supposed Posterior Openings of the Glands. 
According to Harrington, some of the secreted calcareous particles pass back- 
wards in the tunnels, and break through the oesophageal epithelium into the digestive 
tract in segment xiv ; this second outlet for the escape of the secretion has, he adds, 
not attracted the notice of previous workers. If the oesophagus be carefully opened 
along the mid-dorsal line, the milky fluid containing the calcareous particles may 
be seen issuing into the digestive tract from pit-like indentations in the side walls 
of the oesophagus just in front' of the crop. According to Combault, the second 
pair of orifices, discovered by Harrington, are invisible to the eye and to a lens : 
“ nous ajoutons que nous n’avons pu la delimiter nettement. que sur les coupes en 
serie ; on ne peut la voir qu’au microscope a dissection, mais sur une simple vivi- 
section on se rend tres bien compte de son existence a l’oeil nu et mieux a la loupe 
par la fine trainee de liquide trouble qui s’en echappe.” 
We have previously explained that we have never, in numerous series of sections, 
been able to satisfy ourselves that such openings definitely exist ; ruptures, quite 
possibly artificial, may occur in the epithelial lining of the oesophagus, and in this 
way the tunnels may be in communication with the oesophageal lumen. For 
example, a crack in the lining epithelium of the oesophageal lumen, in fig. 13, 
would place one of the tunnels in communication with the lumen. Such ruptures 
may possibly occur at times when the tunnels are full of secretion during life, and 
would be not unlikely to occur when the oesophagus was opened and its interior dis- 
played, owing to the transverse stretching to which the epithelium would be 
subjected. It is in this way that we think the appearances of the escape of milky 
fluid from the hinder end of the glands, as seen by both Harrington and Combault, 
are to be explained. In any case there is no question of the whole, or the majority, 
of the sixty or so tunnels being in communication with the oesophageal lumen at 
their hinder ends— but merely of an occasional one here and there which' bursts, so 
to speak ; and Combault’ s description of the glands as “un organ unique, cavite 
perioesophagienne ouverte aux deux bouts ” is altogether inadmissible. 
An appearance which we met with only in Lumbricus in our own preparations, 
and which is described and explained by Claparede and Combault, is the presence 
of a double circle of tunnels in some sections, one within the other. This led 
Ribaucourt to the mistaken idea of a continuous internally-placed series of tunnels 
and, superposed on this, a separate- series in each of the segments occupied by the 
glands. The condition may be illustrated by text-fig. 1 ; it is a simple consequence 
of the bulging of the glandular mass between the septa, and its restriction at the 
sites of the implantation of the septa ; a section taken along the line a b will 
evidently cut a double or even treble series of tunnels, which will appear as con- 
centric circles. This external lobulation of the glands is very variable, even in the 
same species, as Combault remarks : and he is quite right in maintaining that 
