356 ME. H. M. BEENAED ON THE 



of considerable length. This sucking-apparatus is therefore anterior to the brain. On 

 reaching the central nervous mass, the oesophagus narrows, and its musculature is 

 apparently confined to a layer of circular fibres, which are continued along the whole 

 length. After passing through the nervous mass, it widens again, to end posteriorly in a 

 blind corner (PI. XXXI. fig. 5). The opening into the mid-gut is situated on the dorsal 

 surface of the oesophagus (PL XXXI. tig. 1). No salivary glands enter this oesophagus. 



The specialization of a portion of the CEsophagus into a sucking-apparatus is common to all Arachnids, 

 but a comparison of its position in the different forms leaves little doubt that in Galeodes we find the 

 primitive condition. We find, for instance, the pumping-apparatus contained in a beak in such widely 

 different groups as Galeodes, Thelyphonus *, and Gamasus among the Acarids. The Pseudoscorpions 

 also have a beak, but the sucking-apparatus is condensed at its posterior end, although still anterior to 

 the brain (PL XXVIII. fig. 10). In the Scorpions, in which the beak is much modified, and in the 

 Phalangidse, the sucking-apparatus or its homologue is also in front of the brain. But in these cases the 

 shifting backward of the mouth and the shortening of the beak have also shortened the sucking- 

 aiDparatus. In Phrynus the beak is aborted, and part of the sucking-apparatus is in front of, and part 

 behind, the braia (PI. XXVIII. fig. 7) The Spiders have the sucking-apparatus posterior to the brain, 

 although a few expanding muscle-fibres still remain in front of the brain (fig. 8) . In this case, that portion 

 of the oesophagus which projects backward beyond the central nerve-mass is very considerable. The 

 shifting back of the poi'tion specialized for sucking is no doubt to be traced to the shifting backward of 

 the mouth, which goes furthest in the Spiders t- 



Specialization of the oesophagus itself seems to have gone furthest in some Phalangids, in which the 

 portion of it posterior to the brain is developed into an enormous " crop.'' 



I know of no salivary glands in the Arachnids. The single pair of mid-gut diverticula in front 

 of the diaphragm in Scorpio have been usually taken for such glands, but this is incorrect, the epithelium 

 of this first pair of diverticula not differing in any essential from that lining the following (so-called 

 " liver ") diverticula. 



This absence of salivary glands in the Arachnids is perhaps to be explained in the following way : — 

 In the Insecta, where the mandibles and maxillifi have been much reduced and highly specialized as 

 organs of mastication, grouped closely round the mouth, the acicular glands (from which I would deduce 

 the salivary glands as well as the spinning-glands and tracheae) might easily be specialized as secreting- 

 glands opening within the oral aperture. But in the Arachnids, where the first pair of limbs, and later 

 the second also, are primarily highly-developed seizing-organs (the cheliceree being typically 3-jointed, 

 the pedipalps 6-jointed), and where there is typically no attempt to group them closely around and within 

 the oral aperture as masticatory organs, the absence of salivary glands is what we might expect. It is 

 true, the basal joints of the pedipalps of the Spiders have been secondarily developed as a pair of 

 mouth-organs ; but they are not chewing-jaws. In this case, it is of great interest to find that groups 

 of glands which are probably derivatives of setiparous glands J have been modified to form the so- 

 called " maxillary " glands, whose function, however, is not yet clear. 



This complete absence of chewing-jaws round the mouth in Arachnids (except, according to Mr. 

 Michael, in some Acari) is closely associated with their method of feeding. The Arachnids suck in 

 liquid food by means of their pumping-apparatus. The chelicerse and pedipalps are variously specialized 

 in order to crush the juices out of prey close in front of the mouth. This method of feeding has had 



* Galeodes and TJieh/pJioiiiis are, however, connected by Sc7iho)wtus, 



t Stecker, in his paper on Gihhocellum, figures the mouth behind the basal joints of the pedipalps. This is such 

 an obvious error that one can hardly help taking it for a misprint. 

 X Cf. figs, in Schimkevitch, ' Anatomie de I'Epeire' (62), 



