426 GENEEIL HISTOEY OF THE INFIJSOllIA. 



masses in Melicerta, and found that they disappeared soon after the young 

 animal escaped from the o\a.im. 



Leydig's conclusion, from optical and chemical qualities of the granules, is 

 that they are uiinary or mic concretions, and that the clear space containing 

 them is formed by the end of the intestinal canal, or by the cloaca. To 

 elucidate this view, an analogy is pointed out in the case of those insects 

 which undergo complete metamorphosis, in which solid urinary concretions 

 accumulate in the rectum during the pupa-state, but are evacuated when the 

 insect emerges from that torpid condition. 



The actual secreting organ of these urinary concretions, or in other words 

 the kidney, must, says Leydig, be sought for in the cells of the intestinal 

 wall, which stand out in a knob-like matter. Ehrenberg's account of the 

 " dark bodies " about the rectum of Enteroplea, and of Notommata granulans, 

 favours this opinion ; and the granular heap near the termination of the 

 intestine of the larva of Cydojps may be adduced as another allied fact in 

 illustration of the nature of the bodies in question. Yogt, however, is opposed 

 to this presumed analogy, and states that this peculiar collection in the cloaca 

 of embiyo Cyclopes is originally produced of a green colour, within a sac on 

 each side of the intestine, and when subsequently discharged into the cloaca, 

 is of a yellow hue. These sacs therefore have, in his estimation, rather the 

 signification of a liver than a kidney. The like stnictures are common enough 

 in Vermes. Exceptiilg therefore, Leydig contends, male Rotifers, urinary 

 concretions occur only in the embryo and in the first period after birth, and 

 the existence of a primordial kidney must be admitted as a fact. Cohn has 

 come forward to oppose these views of Leydig, and says that this whole hy- 

 pothesis falls with the proof that in Enteroplea the vesicle with the dark 

 granules stands in no sort of connexion with the intestine, nor, indeed, can 

 do so, as no intestine exists, and it is rather firmly adherent to the outer wall 

 of the testis. To this adverse oj)Lnion Leydig rejoins (Miiller's Arcliiv, 1857, 

 p. 404, and A. N. H. 1857, xx. p. 295) that Cohn's " undoubted proof" is 

 itself an error ; " for the clear space containing the dark granules is not ad- 

 herent to the true wall of the testis, but to that outer envelope which repre- 

 sents the rudimentary stomach and intestine ; or, more properly spealdng, the 

 clear space enclosing the concretion belongs to the abortive alimentary canal 

 itself, which extends from the notch of the rotary organ to the cloacal open- 

 ing, so that Enterop>lea displays the same characters as the other Eotatoria, 

 although this is in complete opposition to the description given by Cohn. My 

 opinion, that the granules in question are uric concretions, is, of course, no 

 more strongly supported by the position of matters detected in Enteroplea 

 than before ; but the objection raised by Cohn appears to be removed. The 

 opinion first put forward by Weisse, which is also favoured by Cohn, that the 

 granules are the remains of unused yelk-masses, I must reject, without taking 

 other reasons into account, Lf only because the vitelline elements and the 

 granules in question have no resemblance to each other, but are perfectly 

 different things." 



Several authors have suggested that the vascular apparatus to be described 

 as a respiratory organ in the foILovving chapter has also in part, or even 

 principally, the fimction of a kidney or excretory organ. These views can 

 be best propounded after the apparatus in question has been described. 



The Yascular and Eespihatoey Systems (XXXVIII. 26 e, i, I ; XL. 1 ?', 5). 

 — ^The existence of vessels subservient to the circulation of a fluid analogous 

 to blood was surmised by Ehi'enberg. Among such assumed structures were 

 the transverse cords to which the semblance of articulation is often due, 

 as well as other similar bands now proved to be muscular fibres of con- 



