137 



arises the extreme difficulty which there is in disentangling 

 the animal and isolating it throughout its length. It requires 

 the exercise of unusual patience to succeed in isolating even 

 a small jJortion of the body. In such conditions, it is easy 

 to understand how difficult it is to study the organisation of an 

 animal, so difficult that one cannot even distinguish with cer- 

 tainty its anterior from its j^osterior extremity. What place 

 should be assigned to this animal in helminthological classifi- 

 cation? It is not without doubt that M. Van Beneclen has 

 placed it among the Trematods. In assigning to it this place, 

 he depended chiefly on, 1st, the extreme mobility of the ex- 

 tremity considered as cephalic, which extends and contracts, 

 shrinks and enlarges successively as is observed in certain 

 Trematods and some Cestoids, such as Caryophyllseus ; 2nd, 

 on the presence in the axis of the body of a contractile vessel, 

 opening very probably on the exterior, and which must be a 

 part of the excretory apparatus ; 3rd, the analogy which this 

 animal presents with certain Trematods, such as Distoma 

 filicolle (Rud.), Distoma Okenii (KolL), which lives in the 

 Brama Rail in cysts similar to those in which Nematobothrium 

 is found. 



Nematobothrium appears then to be an exceptional Trema- 

 tod, of at least a metre in length, having the external charac- 

 ters of certain Nematods, such as Filaria and Gordius, Avhich, 

 like it at the period of sexual maturity, become reduced, in a 

 great measure, to a mere bag of eggs. 



The knowledge of the embryonic form is an element which 

 ought to be of great weight in the solution of the problem 

 relating to the affinities of this singular animal. V. Carus, 

 whilst placing Nematobothrium provisionally among Trema- 

 tods declares that the position of this strange form cannot be 

 determined certainly until the time when the embryonic form 

 is known. ^ 



It is this embryonic form which I propose to make known 

 by this notice. 



I will say a word to begin with concerning the e^^. The 

 egg is of extraordinary minuteness, of oval form ; its long 

 axis measures barely '027 millimetres, its small axis reaches 

 about '020 millimeters. The principle that the number of 

 eggs which an animal produces is indirectly proportional to 

 their dimensions is, completely verified here ; it is neither by 

 hundreds nor by thousands, but by millions of eggs that our 

 animal reproduces. The calculation is easy to make ; know- 

 ing the number of eggs contained in a given length of the 



^ 'Haudbuch der Zoologie,' von J. V. Carus und Ad. Gerstaecker, iiBd., 

 p. 480. 



