Oab ASTACOCEOTON, A NEW TYPE OF ACAEID^ 



and ;ui achromatic network having a prevailingly radial ai-rangement. The nar- 

 row apical part of each cell is virtually its duct and pierces the cuticle of the 

 heginning of the main duet to open into its lumen. In large adult animals the 

 structure becomes complicated by the main duet receiving a tributary duct, which 

 arises from a small cavity of the nature of a secondary lumen in the interior of 

 the more ventral part of the gland. 



The duct, a narrow tube with a cuticular lining, runs straight forwards to 

 join those of the two glands yet to be described. 



The reniform glands (PL xxxvi., fig. 10 and PL xxxvii., fig. 13, S2) ai-e 

 much smaller than the dorsal — only about .07 mm. in diameter — and lie opposite 

 the middle of the dorsal glands and external to the latter. The main part of 

 each is a rounded body containing a number of nuclei which, though lai-ge (.01 

 mm. in diameter) compared with those of most of the other tissue-elements, are 

 small in comparison with those of the cells of the dorsal glands. 'I'hese nuclei 

 ai-e quite irregiilarly arranged and the cells which they represent are not always 

 clearly distinguishable. In the substance of the gland are small vacuoles and 

 canals and a narrow central lumen, not distinguishable in all cases, from which 

 the duct arises. The latter runs forwards to join the other salivary duets. 



The third pair of glands in Astacocroton belonging to- the "salivary" group — 

 the anti-coagidin glands — undoubtedly correspond morphologically to the "tubular 

 salivary glands" of Michael, the "glandes tubulaires" of Thor, the "sehlauch- 

 formige Driisen" of Schaub (1888). But in Astacocroton these glands present 

 features of sig-niflcance which, so far as I can ascertain, have not been observed 

 in any other Acarid. Each gland (PL xxxvi., flg. 10, co) begins in front close 

 to the corresponding dorsal and reniform glands, external to the former and 

 separated from it by the muscles running from the dorsal body-wall to the base 

 of the rostrum, somewhat ventral to and behind the latter. The anti-eoagulin 

 gland begins in front in an elongated vesicle or reservoir with, in some cases, a 

 considerable lumen and comparatively thin walls. This gives ofd, in front, a 

 duct which runs inwards and forwards to join those of the reniform glands. 

 Posteriorly it is produced into a tube which is thrown into several folds, and 

 undez-goes several dilatations, 'llie chief of these dilatations has a funnel-like 

 appearance in transverse sections. What represents the mouth of the funnel, 

 which faces inwards, is closed by a thin wall of small cells. I'he remaining 

 walls of the "funnel" are relatively thick and composed, like the rest of the 

 organ, of cells without definite boundaries, recognisable only by their nuclei 

 which are distinctly smaller than those of the reniform glands. The reservoir 

 passes into a wide tube which is twisted on itself and this divides behind into 

 two narrow tubes (about .03 mm. in diameter) which run backwards in the 

 wall of the mesenteron (PL xxxvii., fig. 15, a.c.g.) sometimes close together, 

 sometimes wider apart. Finally, far back in the wall of the mesenteric diver- 

 ticulum, the two tubes unite and terminate; in other words, the two tubes are in 

 reality a loop. In some series there is a short anastomosis about the middle. 



The meaning of the special form of the tubular glands and the peculiar 

 position of their loops might be conjectured; but to my mind at least it is 

 rendered perfectly clear by the evidence of some of my series of sections. In 

 these, not only is the mesenteric epithelium altered and partly dissolved away 

 along the track of the loop, but a definite effect has evidently been in the act 

 of being produced on the blood in the mesenteric lumen, an effect which is strictly 

 ■ limited to this track and extends throughout its length. The nature of this 

 effect is difficult to describe : it is as if a cloud of clear unstainable liquid were 



