198 MR. A. D. MICHAEL ON AN [Mar. 5, 



packed, elongated cells of about "01 mm. diameter, and in section 

 exhibit similar cellulation all through ; they are quite solid without 

 lumen ; but I have not been able to trace any duct from them. 1 

 thought at one time that they probably discharged into the posterior 

 part of the tubular salivary glands ; but after careful investigation 

 I am not, up to the present, able to state that this is the case, 

 although the two organs are in tolerably close juxtaposition ; and 

 the function of the glands therefore remains uncertain to me. 



The Palpal Organs (Plate VIII. fig. 22). 



These organs might probably be included in the last section as 

 glands of unknown function, but I do not wish to pledge myself 

 to the assertion that they are glands, although I incline to think 

 so. They are largish paired organs, one on each side of the body ; 

 the posterior portion is an elongated lobe with a rounded hinder 

 end ; about a third of the length of this lobe (the posterior third) 

 lies under the brain, but is not in any way connected with it, there 

 is a separate nerve from brain to palpus. The lobe runs in an 

 almost direct course from below the brain to the palpus, but it 

 diminishes considerably in diameter before reaching that appendage, 

 and where it enters has less than one third of the diameter of 

 the thickest part of the lobe. Within the first joint of the 

 palpus the palpal organ swells out again and forms a second elon- 

 gated lobe, not nearly so thick as the first ; at its distal end this 

 bends slightly downward, and enters the second joint, where it 

 again diminishes in diameter, and then runs forward until nearly 

 the distal end of the palpus, keeping an almost uniform thickness 

 (the anterior part is not shown in the figure). The organ is com- 

 posed of large irregularly-placed cells, as far as can be judged 

 from the nuclei, which are few but very distinct and of considerable 

 size ; but I have not been able to detect the lines of demarcation 

 between cell and cell in any of my preparations. 



The organ is solid, i. e. there is not any lumen, and I have not 

 been able to trace anything like a duct from it. I am not aware 

 of anything which has been described in the Acarina which can be 

 identified with it or considered the homologue of it ; nor have I 

 ever seen such an organ in any other species that I have examined : 

 the structure most resembhng it, that I am acquainted with, in 

 the Acarina is the spinning-gland partly in the palpus of Tetra- 

 nychus ; but the present species is aquatic and there is not any 

 reason to suppose that it has any power of spinning; moreover 

 the palpi are not furnished with a spinneret, such as is found in 

 Tetranychus. The palpus is almost certainly a raptorial organ, it 

 assuredly is not tactile ; but there is not any poison-fang or spine 

 that I can discover, and the mandibles are evidently the killing- 

 organs. For these reasons I think it best not to suggest a function 

 for these palpal structures and to leave the matter for future 

 investigation. 



