INTERNAL ANATOMY OF BDELLA. 489 



■word ingluvies is more properly used for a crop ia the direct liae of the caual, I propose 

 the name of " receptaculiuii cihi " for the stalked food-sacs. 



The remainder of the oesophagus does not appear to require any special notice ; it 

 terminates, as usual, in the ventriculus. 



The Ventriculus (fig. 6) is greatly flattened dorso-ventrally, forming a shallow layer 

 near the dorsal surface; it is far best studied in young specimens, as in older ones, 

 where the ventriculus is more distended both by the food in the lumen and by that 

 which has been absorbed by the cells which form the walls of the organ, and where the 

 genital organs are fully developed, the ventriculus is forced into every availalole space 

 and its true foi*m is difficult to follow : this difficulty, however, does not exist in the 

 younger creatures. Fig. 6 is drawn from a female of B. Basteri, matu.re but only 

 lately emerged from the nymphal skin. It will be seen fx'om this drawing that the 

 ventriculus consists of a short, more or less elliptical sac with a slight median projection 

 forward, and having from its antero-lateral edge two rather short, paired caecal 

 diverticula directed forward, and from its postero-lateral margin two broad and long 

 paired caeca directed backward. These last-named caeca have the inner edge simple and 

 almost straight ; but the outer edge is divided into rounded lobes, w^hich diminish 

 in size from liefore backward — /. e. the anterior lobe is much the largest and the posterior 

 mucli the smallest. Thus the whole organ forms a sort of irregular, comi^ressed, and 

 elongated horse-shoe. 



The histology of the ventriculus is, as might be expected, very similar to that described 

 by Heukin in Trombidmm fuUginosum ; of course there are some differences. The 

 exterior of the organ is a fine tunica propria, so delicate that it is usually impossible to 

 dissect the ventriculus out without breaking it ; on the inner side of this tunic is a single 

 row of large columnar epithelial cells with small oval nuclei, about 8/i in diameter, very 

 clearly nucleolated, placed near the exterior ends of the cells. The cells themselves 

 vary greatly in form and size in difl'erent parts of the ventriculus, and of course in 

 diffei'ent individuals ; the cells on the dorsal side of the ventriculus usually average 

 longer than tliose on the ventral side. In an adult weU-fed male specimen of B. Basteri 

 the cells are ordinarily from about "0 J. mm. to abou.t "12 mm., in the female they are even 

 longer. The exterior portion of the cell is filled with fine reticular protoplasm ; the 

 interior part, next the lumen, is generally crowded with food-droplets, precisely similar 

 to the contents of the sucking-stomach ; this is even more marked in the female than the 

 male, liut in both sexes the inner portions of the cells are usually almost full of them. 

 Digestion appears to be iutra-cellular : no food-ball or mass, and indeed very little food, 

 is usually found in the lumen of the viscus, unless tlie creature has been killed almost 

 when feeding ; it is all in the cells. The process described by Hcnkin, that the inner 

 ends of some of the cells get more or less filled with a granular dark material, and then 

 are constricted ott* and fall into the lumen of tlie viscus, occurs also in Bdella, but 

 apparently much less frequently and to a much smaller degree than in Henkin's Acarvs. 



Excretory Organ. — We now come to the subject of the hind-gut, h\xi in all the 

 Trombidiuiu-grou]) of Acari it is impossible to treat this separately from the excretory 

 organ ; the two are either identical or so intimately connected as to render it necessary 



