294 MK. GEOEGE M. THOjMSON ON A FEESHWATEK 



if capable of very considerable backward and forward movement. At about t\^ o-tbirds of 

 its lengtb, or just about tbe first abdominal seg-ment, it bears on its upper surface a sbort 

 oval csecum — in large specimens about 2 mm. long, — directed forward (PI. III. fig. 2). 

 Tliis organ is evidently an excretory gland. Its cavity is densely lined with tube-sliaped 

 cells placed vertically to tbe walls, leaving a hollow space in tbe interior, which is 

 partly tilled with loosely-interwoven elongated and pointed cells, and communicates by 

 means of a sbort duct Avith the intestine. At about tbe extremity of the antepenulti- 

 mate segment of the abdomen the intestine bears on its upper surface another csecum, 

 shorter than the first and directed backward (fig. 3). This is also lined with glandular 

 tissue arranged in the same manner as in the anterior one, and has a central duct. Tlie 

 function of both these organs is probably urinary. In tbe last abdominal segment the 

 intestine contracts sharply to less tban half its previous diameter, and, entering the telson, 

 bends abruptly upward and backward, and then passes out nearly straight to the anus, 

 which is in the form of a longitudinal slit. Where it contracts the wall is surrounded by 

 a coat of muscles arranged in an annular manner. 



The liver is quite difi"erent in its structure from the corresjionding organ in any other 

 Crustacean with wdiich I am acquainted. Ow ing to tbe very soft tissue of which it is com- 

 posed, especially in its anterior portion, and its consequ.ent state of disintegration in all 

 my specimens, I have been able to make out only a portion of its structure. It consists of 

 a number of slender cylindrical tubes, lying horizontally, but slightly interwoven in the 

 body-cavity, above and on both sides of tbe alimentary canal, and reaching back to half- 

 way betw een the intestinal caeca. In one specimen I traced as many as eighteen of these 

 tubes forward to about tbe posterior end of the stomach, but failed in every instance to 

 find any duct or opening into the alimentary canal. These tubes are of a yellowish 

 straw-colour in ordinary spirit-specimens. Their posterior portions, when considerably 

 magnified, exhibit at the extremity a mass of slightly elongated pointed cells, thickly 

 charged with granular contents (PL XXVI. fig. 9). At a short distance from tbe end a 

 duct arises, the cells all round it, winch line the w'alls of the tube, being arranged in a 

 more or less vertical direction. 



Excretory organs. — My identification of the so-called " green gland " or renal organ 

 characteristic of all tbe higher Crustacea is not satisfactory, if indeed it exists at all. I 

 have not identified it in dissected specimens, but in one or two sections I have observed 

 ■what appears to be a small mass of glandular tissue lying in front of and partly below 

 the anterior lobes of the stomach and close up to the bases of the lower antennae. At 

 the same time I have not found any duct by -which its excretions are liberated. It is 

 just possible that I have mistaken for this the somewhat disintegrated tissue of the pre- 

 oral ganglion ; but if so, its connexion with the large nerves supplying the eyes has not been 

 traced. It is perfectly possible that the organ is wanting or only exists in a rudimentary 

 state, especially if the intestinal caeca usurp its functions, as I have surmised. 



Circulatory apparatus. — My observations on this part of the anatomy are A'ery frag- 

 mentary, but they are suflicient to attest the primitive character of Ana.spides. 



The heart consists of a long simple tube, apparently little dilated in each body- 



