10 



we have to do with something also found in other forms ; in the 

 duodenum of the frog he described analogous cells 36). F r e n z e 1 

 also calls them ,,Sekretzellen". 



The argument of Herouard that these groups of cor- 

 puscles do not have any duct and consequently can not have 

 excretory function, is of course valueless. His opinion that they 

 would serve for the transport of food, is not proved by any 

 experiments. 



4. BIOLOGY. PREY. 



The old story of the starfish devouring a bivalve, is too old 

 to be repeated again in full detail. As early as 1826 Eudes- 

 Deslongchamps 38) already described the process in the 

 charming, primitive way of the observing biologist. He found 

 starfishes on groups of Mactra stultorum. L. in the act of 

 devouring this prey. „}e remarquai qu'elles avaient introduit 

 entre ces valves de grosses vesicules arrondies, a parois tres 

 minces et remplis d'un liquide transparent." Here he means the 

 stomach-edge of course, which is inserted between the valves 

 and applied directly to the soft parts of the prey. He takes 

 them for sacs in which there is a little opening through which 

 the liquid content, a "humeur engourdissante", drips out gradually. 



The opening of such bivalves is still always a problem when 

 we take in consideration the enormous force of the adductor 

 muscles of these animals. Many authors believe that a toxic 

 substance of some kind helps here — this problem will be 

 discussed in a separate chapter — , Schiemenz (Mitt. d. 

 deutschen Seefischereivereins. XII. 1896. p. 102. Quoted from 

 Mc. Bride in : Cambridge Natural Hist.) has figured out the 

 dynamics of the process. He showed, 1. that while a bivalve 

 can resist a sudden pull of 4000 grams, it yields to a long 

 continued pull of 900 grams ; 2. that a starflsch can exert a pull 

 of 1350 grams ; 3. that a starfish is unable to open a bivalve 

 unless it can raise itself into a hump so that the pull of the 

 central tube feet is at right angles to the prey. To prove this 

 he mentions the interesting case of a starfish, kept between 

 two glass-plates, walking around all day dragging about a bi- 

 valve, but unable to open it. 



Mc. Andrew and Barret 2) soon found that the „vesi- 

 cules' ' observed by Deslongchamps, are nothing else but the 

 stomach, protruded as it is filled with the perivisceral fluid. It 

 has considerable motility and can even penetrate to way up in 

 the shell of a Littorina, as I could observe myself in one case. 



About the completeness of this ,, extra-intestinal digestion 

 (Jordan)", practically nothing is known. Whether it is complete 

 as in Carabus 67) and Dytiscus-larvae or incomplete as in the 

 case of the mesenteric filaments, ,,Saeptalrander" of the Actinians, 



