BY W. A. HASWELL. 337 



passing out into the faintly stainable granular plasma of tbt' blood-food along 

 the course of the loop. The conclusion seems unavoidable that, though the 

 tubular glands have their own ducts which carry their secretion into the mouth 

 through the common salivary duct, a part of the secretion diffuses from the 

 looped tube into the lumen of the mesenteron. 



"I'hat an anti-coagulin is produced in the digestive system of Astacocroton 

 has not been proved. In the ticks Ixodes and Argas, Sabbatani, in the case of 

 the former, and Nuttall and Strickland (1908) in the ease of the latter, demon- 

 strated its presence experimentally. But since the question presented itself I 

 have not been able to muster sufficient fresh material to render such experiment 

 practicable. However, the fact that the blood-food does remain uncoagulated in 

 all but a few exceptional cases seems to prove that an anti-coagulin is produced. 

 And the very peculiar relationship found to exist between the loop of the tubular 

 gland and the mesenteric epithelium seems to point to that gland as the most 

 probable source of the ferment. 



8. The integument ; the so-called fat-body. 



The cuticle of the general surface is very thin — about .00143 mm. — It con- 

 sists of two layers — the outer homogeneous, the inner with an obscure structure 

 of vertical pillars, with an undulated inner surface. That of the capitulum is 

 nearly twice as thick. The underlying layer — epidermis — is thinner than the 

 cuticle, and in the adult animal no longer exhibits a cellular structure. Below 

 the epidermis, in the body-cavity are a good many leucocytes, about .01 mm. in 

 diameter when rounded oft, filled with small granules, which have a strong affinity 

 for eosin or erythrosin. 



Within, on the dorsal side, is a layer (PI. xxxvii., figs. 15 and 16, /) not 

 quite continuous, of sharply defined cells of irregailar shape and size, averaging 

 about 0.02 mm. in diameter with nuclei of about 0.01 mm. and nucleoli of about 

 0.005 mm. or rather less. 



These are the cells figured and described in .T.rombidium by Henking (1882, 

 Plate xxxiv., fig. 10) as "Fettkoriserzellen." They lie in close contact with the 

 dorsal side of the mesenteron and excretory organ, and in front of tliese over the 

 dorsal glands. Thor (1904, p. 37) regarded them erroneensly as young ova. 



9. The Excretory Organ. 



This is a median sac (PI. xxxvii., figs. 14-16, ex) extending throughout the 

 length of the body towards the dorsal side, and opening on the exterior by the 

 small excretory aperture (PL xxxvi., fig. 1 and Fl. xxxvii., fig. 18), situated a 

 little distance behind the posterior end of the genital slit. In front it divides 

 into two branches which curve outwards and forwards each running in an almost 

 transverse direction in a fold of the wall of the mesenteron to terminate 

 blindly over th% eoxal glands. Behind, before narrowing to open on the exterior, 

 it gives off a pair of short lobed caeca. Its general appearance in the living 

 animal has already been referred to. In sections the main part of the organ is 

 seen to be a laterally compressed tube with a narrow vertical lumen expanding 

 somewhat dorsally where it lies immediately below the dorsal body-wall. It is 

 intercepted between the two enteric caeca, with the inner walls of which it is 

 intimately connected, and abuts below on the wall of the uterus. 



The wall of the organ consists of two layers only — an internal epithelium 

 and an external supporting layer or basement-membrane. The epithelium is a 

 single layer of cells flattened for the most part and not sharply marked off from 



