MORPHOLOGY OF MBLIBB 547 



Nesselkapselsiicken commimiciren konnen Diese Form der 

 " Leber " macht wahrscheinlich, dass sie nicht etwa bloss ver- 

 dauende Secrete absondert, sondern sich auch selbst bei der Ver- 

 dauimg und bei der Resorption der Producte der Verdauung be- 

 theiligen wird. In der That weiss man schon lange, dass bei 

 den Nudibranchiern Speisebrei in diese Verastelung des Darmes 

 hineingelangt ; aber auch fiir eine Form mit ganz compacter 

 Leber, namUch fiir Helix pomatia, wurde klirzHch der 

 Beweis erbracht, dass in der That in der " Leber " Aufsaugung 

 Oder Resorption der verdauten Nahrung stattfindet.' 



Quatrefages (1844, 1844 a, 1848) maintained that the liver 

 in Nudibranchs is of a threefold function ; hence his term 

 ' Plebenterism ' to designate that species of gradation which 

 consists in the imion of different functions in one system of 

 vessels. That is, he maintained the absence of anal opening, 

 heart, and blood-vessels, adopting the term gastro-vascular 

 system introduced by Milne H. Edward (1842, 1845) for the 

 digestive organs in the family A e o 1 i d i i d a e , the true 

 significance of which has since been the subject of much 

 controversy. It is now, however, a well-established fact that 

 the group of molluscs with which de Quatrefages dealt 

 (Aeolidiidae) has a well-established circulatory system, 

 i. e, heart and blood-vessels, and alimentary tract with anal 

 opening. The liver branching off from the digestive tract forms 

 into many parts and ramifies to various parts of the body. 

 One unquestionable function of the liver, as far as Aeolidia 

 is concerned, is an exit for harmful and indigestible parts taken 

 in with food (Alder and Hancock, 1845 ; Glaser, 1903 ; Hert- 

 wig, 1912). Glaser describes the hepatic caeca as secondary 

 exits in nudibranchs which feed on hydroids whose nemato- 

 cysts produce indigestible formic acid ; the mollusc rids itself 

 of its useless stomach contents through these secondary 

 openings of the liver-branches which end in the dorsal papillae. 

 M. leonina does not feed on hydroids, but on crustaceans 

 (Agersborg, 1916, 1919, 1921, 1921a, 1922a, 1923); and, 

 although the hepatic system is tubular (PL 30, figs. 25, Cshb, 

 31, Ch ; PL 33, figs. 51, 53), it does not end with openings 



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