458 Aquiferous and Oviducal System in Lamettibranchiata. 



and yet free from any admixture of its constituent elements (as 

 the microscope will show), that we find the capillary network 

 (shown to be in connexion with the oviducal outlet whilst clear 

 of the terminal cseca) of the gland to attain its maximum deve- 

 lopment. Now this area is the area also of maximum disten- 

 tion in the distended foot. If in a Unio which has been in- 

 jected from the blood-vascular system and from the oviducal, 

 both with differently-coloured injecting-fluids, a portion of the 

 injected tissue be taken from this area and placed under one of 

 the higher powers of the microscope, the fluid which has been 

 thrown in by the oviducal orifice will be seen to be contained in 

 tubes as well and sharply defined as those of the capillaries 

 which the other injected fluid will show to be in connexion with 

 the blood-vessels. 



Whilst the analogy of the Echinodermata and many Annelids 

 does away with any a priori improbability which may have 

 seemed to attach to the possession by these mollusks of the sys- 

 tem of tubes the existence of which we have been striving to de- 

 monstrate, the homology of the Brachiopoda furnishes us with 

 a strong a priori presumption in favour of the correctness of 

 our view. On the other hand, we cannot forbear pointing out 

 the great improbability which must attach to a view which sup- 

 poses a fluid of such morphological and such chemical charac- 

 ters as is the blood of the freshwater mussel to be diluted as it 

 must be diluted on the hypothesis of the blood-vessels being the 

 agents by which the animal voluntarily distends itself often to 

 thrice its undistended bulk. How do the blood-corpuscles which 

 we may take from the interior of the animal's heart behave when 

 thus mixed with water under the microscope * ? But it is not 

 upon considerations such as these that we would lay most weight, 

 but upon the evidence which injections of the several systems 

 furnish to the unassisted eye, and upon the confirmation of that 

 evidence which microscopic inspection furnishes. 



* " Reagentien, wie ein Ueberschuss von Wasser, verdiinnte Essigsaure, 

 Ibsen bei der ersteren Art (Blutkorperchen) den scheinbar festen Inhalt 

 auf, und lassen den Kern, wie die eingescblossenen Kornehen, deutlich 

 hervortreten. Ihre baufigen Formveranderungen, z. B. die " spiessigen 

 hirscbgeweibabnlichenFortsatze/'welcbe sie treiben,h'angen vonunvermeid- 

 lichen Diffusionverhaltnissen ab, welchen sie bei der grossen Wassermenge 

 gegeniiber ibrer verb'altnissmassig geringen Anzabl ausgesetzt sind. Wah- 

 rend A. Ecker dieselben durch eine Bildung von Vacuolen, in Folge deren 

 Vergrosserung sie einreissen, zu erklaren sucbt, bait Lieberkiihn diese 

 Zellenbildungen fur Amoben mit selbstandigen contractilen Bewegungen. 

 In innigem Zusammenhang mit diesen Erscheinungen steht das leichte Aus- 

 treten des Zelleninhalts, welcher bisweilen in hellen und hyalinen Tropfen 

 herumschwimmt, ja nicht selten geht ein Zerf alien desselben in zabbeicbe 

 kleine Tropfchen noch innerhalb der Zellen vor sich, welche dadurch ein 

 maulbeerartiges Anseben bekommen, ebenso vereinigen die ausgetretenen 

 Sarcodetropfen diese Korpercben zu den oben erw'ahnten Kliimpchen urid 

 Flockcben," — Von Hessling, loc, cit. pp. 219, 220. 



