134 



DESCRIPTIONS OF PREPARATIONS. 



as the nucleus of a new style. The chemical reactions of both bodies prove their 

 albuminoid nature. 



The liver in Lamellibranchiata secretes a diastatic as well as a peptic or 

 tryptic ferment ; of the two latter, sometimes apparently only the former, as e. g. 

 in the Oyster and Edible Mussel, or both, as in the Scallop (Pecten Jacobaeus) in 

 which the extract is active in alkaline, neutral and acid solutions alike. The 

 liver contains no calcareous cells, only granular and ferment cells (see pp. 116-17). 



The heart consists of a median, thick-walled ventricle, and a thin-walled 

 auricle on either side. The auriculo-ventricular apertures are valved. An aorta 

 arises from both ends of the ventricle; the anterior passes above, the posterior 

 below the intestine. The blood spaces are for the most part lacunar, but vessels 

 are found in the walls of the intestine, labial tentacles, and gills (?). There is a 

 median venous sinus lying between the two nephridia. From it blood passes to 

 the nephridia, thence to the gills, and so to the auricles. The blood is colourless, 

 and has colourless corpuscles. The pericardium surrounds the heart. It com- 

 municates with the glandular portion of the nephridium, two apertures at the anterior 

 end leading one into each gland. It is thus directly connected with the exterior. 



The renal organs or nephridia (= organs of Bojanus) are paired. They lie 

 ventrally to the pericardium, and are divisible into a duct or non-glandular, and 

 a secreting or glandular portion. The former opens by a pore at the side of 

 the body, and is covered by the inner lamella of the inner gill, where it is attached 

 to the side of the visceral mass. It lies under the pericardium, and opens 

 posteriorly into the glandular portion which underlies it. There is a communica- 

 tion anteriorly between the ducts of opposite sides. Other communications have 

 been stated to exist between the ducts and the organ of Keber. The glandular 

 portion contains numerous lamellae, and is greenish in life. It communicates 

 anteriorly with the pericardium (supra). The outer surface of the ducts has a 

 cylindrical epithelium ; the inner has an epithelium, of several layers, the outer- 

 most cells rounded and ciliated. A similar ciliated epithelium exists in the 

 glandular portion of the organ. The superficial cells of the latter contain yellow- 

 brown urinary concretions. Guanin not uric acid is stated to be found in them. 

 The relations of the organs are illustrated in PI. vii. fig. 4. Kollmann has recently 

 described ciliated funnels (nephro-stomata ?) on the lamellae of the glandular 

 portion of the organ. Their number appears to be great, as many as 200 in an 

 Anodonta specially examined from this point of view. The funnels, however, 

 appear to be blind, and not to lead into any system of canals or into the blood- 

 lacunae of the lamellae into which their blind ends project. 



The generative organ of each side opens by a pore in front of the open- 

 ing of the nephridium. The organs are simple racemose glands, and alike in 

 both sexes. They can only be distinguished by the characters of their products. 

 The testis, however, is whitish in colour ; the ovary reddish. In the few herma- 

 phrodite forms the gland may be divided into a distinct male and female part, 

 e.g. Cydas\ or the two elements, male and female, may lie side by side in the 

 same caeca as in Ostrea edulis. In the case of the Oyster the two generative 

 products ripen at different times, and hence self-impregnation does not occur, 

 a rule which obtains in most hermaphrodite animals. Anodonta appears to 

 be occasionally hermaphrodite. 



