248 ]\fr. A. Tulk on the Anatomy o/ Phalanglum Opilio. 



of the three anterior pairs of small cseca are three other dilata- 

 tions : the two anterior (PI. IV. fig. 17. hr/), one of which is 

 slightly longer than the other, appear to nnite and open by a 

 common neck into the intestine ; the posterior, nearly twice their 

 length iff), curves backwards, and terminates distinct from the 

 other two. There are thus thirty cfcca to the alimentary canal of 

 P. Opilio ; not thirty-one, as stated by liamdohi', who represents 

 an azygos pouch as arising between the two most anterior cseca, 

 but which, with Treviranus, I have been unable to detect. Poste- 

 riorly, the alimentary canal terminates by a short and wide rec- 

 tum (r), which opens externally between the last of the dorsal 

 and ventral segments of the abdomen, the anus being situated 

 upon a level with the latter. 



With regard to the probable function which the above nume- 

 rous csecal appendages may perform in the process of digestion, 

 it is difficult to offer any very satisfactory conjecture. Charac- 

 teristic as they appear to be in general of the alimentary canal in 

 those creatures which live exclusively upon the fluids of others, 

 such as the Planaria, the leech, the Aphrodite, the Nicothoe, and 

 in the Arachnida, the spiders and scorpions, with the Acaridean 

 genera Ixodes and Gamasus, one would have expected to have 

 found these organs less developed in the present group, from the 

 very circumstance, already stated, of their mouth being adapted 

 also to the purposes of mastication ; and yet, strangely enough, 

 their number and size is greater even than what is met with in 

 the purely blood-sucking Araneidans. By some ^Titers the parts 

 in question have been regarded as so many reservoirs, in which 

 the nutriment may be stored up, so as to serve the animal for 

 some length of time, but this is an opinion which seems scarcely 

 applicable to Plialangiurn, from the following facts. The dilated 

 stomach usually contains a smooth, black and oval mass of excre- 

 mentitious matter (PI. IV. fig. 20. /, nat. size), and what is sin- 

 gular, this {e, magnified) is inclosed in a distinct membranous 

 covering [m) which sui-rounds it continuously, and is thro\^Ti 

 into slight transverse folds. The mass still adheres together 

 after the latter has been removed, and, iipon being broken up, 

 is found to consist of the debris, or undigested hard parts of va- 

 rious insects, such as the eyes, legs, wings, antennae, &c., imbedded 

 in a granular substance. If, on the other hand, the contents of 

 the cseca be examined, it will be seen to be a granular substance 

 also, exhibiting under the microscope a similar appearance to the 

 above, with this difference, however, that along with it no traces 

 of organic remains can be detected. May it not be inferred from 

 this, that one office at least of the cseca is to secrete this matter, 

 which, discharged into the stomach, agglutinates the particles of 

 food together ? The investing membrane of the fseces may serve 



