232 



REN. 



PART I. 



RENAL ORGANS IN THE LOWER ANIMALS. 



Under this head we purpose to refer briefly 

 to such facts in the anatomy of the urinary 

 organs of the lower animals as will serve to 

 render more intelligible the structure and office 

 of the human kidney. 



Invertebrata. That the excretion of urine 

 is a function of great importance is sufficiently 

 manifested by the fact that a special organ for 

 the performance of this office is found in ani- 

 mals very low in the scale of organization. 



In insects the urinary glands are usually in 

 the form of long and delicate tubes, but some- 

 times present the structure of groups of round 

 vesicles, as in the Carabus,in which the common 

 duct terminates in a small dilatation ; the 

 urinary bladder is likewise present in the water- 

 beetles. The excretion is poured into the 

 termination of the intestine, or evacuated con- 

 tiguous to the anus.* 



In the Arachnida, " two long and slender 

 urinary tubes communicate with the beginning 

 of the coecum, which seems to stand to them 

 in the relation of an urinary bladder," 



In the Lamellibranchiata, " the returning 

 veins of the body form a remarkable plexus at 

 the base of the gills near the pericardium, 

 which assumes the form of a distinct glandular 

 organ in the higher Bivalves. The secretion 

 of this venous body abounds with calcareous 

 particles, and the gland was called by Poli the 

 secreting organ of the shell. Modem analysis 

 has detected a large proportion of uric acid in 

 the peritoneal compartment enclosing this 

 venous plexus, and has thus determined it to 

 be the renal organ." -f- 



In the Gasteropoda, the urinary gland is a 

 follicular organ attached to the walls of the 

 branchial cavity. In some species of Palu- 

 dina the duct dilates to form a small recep- 

 tacle. 



Among the Cephalopoda, the Nautilus pre- 

 sents the supposed analogues of the urinary 

 organs in the form of clusters of glandular 

 follicles of a simple pyriform figure, three 

 clusters of such glands contained in mem- 

 branous follicles being situated on each of the 

 four branchial veins. The walls of the re- 

 ceptacles exhibit in some parts a fibrous tex- 

 ture, apparently for the purpose of compressing 

 the follicles and discharging their secretion 

 into the branchial cavity by apertures at the 

 base of the gills. The analogues of these 

 organs exist in the higher Cephalopoda, in 

 which they are considered to act as kidneys 

 by Mayer; and Prof. Owen remarks J, "it 

 is more philosophical to conclude that the 

 organs of so important an excretion should be 

 present in all the class, than that they should 

 be represented by the ink-gland and bag, 

 which are peculiar to one order." 



Vertebrata. In Fishes the kidneys are 



* Professor Owen's Lectures on Comparative 

 Anatomy, 

 t Ibid. 

 J Lectures on Comparative Anatomy. 



long and narrow ; they are situated on each 

 side of the mesial line, immediately beneath 

 the bodies of the vertebrae, and extending 

 through the whole or the greater part of the 

 dorsal region of the abdomen. They are 

 usually broadest and thickest anteriorly, while 

 they become smaller and approach each other 

 as they extend backwards. Sometimes a 

 single common ureter quits the coalesced 

 hinder ends of the kidneys. In some species 

 the kidneys are thickest at their posterior 

 ends. They have not a well-defined capsule, 

 but their ventral surface is immediately 

 covered by an aponeurotic membrane, against 

 which the peritoneum and the air-bladder, 

 when present, are applied. The renal tissue 

 presents a uniform appearance without di- 

 vision into a cortical and medullary portion. 

 The urinary tubules pass immediately into 

 the ureter without the intervention of a pelvic 

 cavity. Malpighian bodies exist in the kidneys 

 of the fish as in those of 'the higher vertebrata ; 

 the structure of these bodies will be fully 

 explained in a subsequent part of this article. 

 The kidneys are supplied throughout their 

 entire length by numerous small branches from 

 the abdominal aorta. In addition to the ar- 

 terial blood thus supplied to the kidneys, 

 these organs also receive a large quantity of 

 blood from the veins which proceed from the 

 posterior part of the body. This peculiar 

 system of veins, which was discovered by Bo- 

 janus, and more fully described by Dr. Lu- 

 dovic Jacobson*, is found in birds and reptiles 

 as well as in fishes. In its primary form it 

 undergoes, according to Jacobson, three de- 

 grees of modification. The^n-^ modification 

 exhibits the following form : From the skin 

 and muscles of the middle part of the body 

 branches arise, which form several trunks, 

 passing separately to the kidneys. 



In the second modification, the veins which 

 return from the posterior part of the body are 

 received into this separate system.* The 

 caudal vein, which brings back the blood from 

 the skin and muscles of the posterior part of 

 the body, divides into two branches, which, 

 having received some veins returning from the 

 middle part of the body, pass to the kidneys of 

 each side, and distribute their branches in the 

 substance of these glands. 



In the third modification, the veins of this 

 system are formed in the same manner as in the 

 preceding, excepting that the caudal, or other 

 vein returning from the posterior part of the 

 body, gives off a branch to the vena portce. 



The blood, returning from the middle and 

 posterior part of the body in the first and second 

 modification of this system, is conveyed only 

 to the kidneys ; but in the third it is divided 

 between the kidneys and the liver. The 

 inferior vena cava of the common venous 

 system, in the second and third modification 

 is composed of the veins returning from 

 the kidneys and testicles or ovaries. In the 

 first modification, the caudal vein receives 

 the veins returning from the kidneys, is united 



* Edinburgh Medical and Surgical Journal, 

 vol. xix. 



