Prof. E. Claparede on the Structure 0/ //ie Annelida. 351 



In contrast to this radically false description, let us see liow 

 the circulation is effected in the normal branchia of an Annclide. 

 There cannot be in a regular way any mixture of arterial and 

 venous blood ; in fact the artery travels as far as the extremity 

 of the branchia, where it bends round to return as a vein. The 

 vein and the artery are exactly parallel to each other. Through 

 the whole length of the branchia these two vessels are put in 

 communication by a double series of vascular loops, which pass 

 into the subcuticular layer, and which are subjected with the 

 greatest facility to the action of the water charged with oxygen, 

 through the very thin cuticle. As to the contraction of the 

 supposed ampullae, there is nothing of the kind. Some genera, 

 such as the Terebellfs and the Telethusce, for example, certainly 

 present rhythmical contractions of the whole branchia, but not 

 of the vessels themselves. This fact, however, is exceptional. 

 The family Serpulea alone presents in the structure of its 

 branchise a distant resemblance to the description of M. de 

 Quatrefages. In these Annelides the artery is continued directly 

 into the vein at the base of the branchiae, and from their point 

 of union starts a single vessel, which penetrates into the 

 branchia and sends a csecum into each branch of it. But 

 M. de Quatrefages describes in the secondary branches of the 

 branchiae of the Serpulea all his apparatus of ampullae, of which 

 not the least trace exists. The caecal vessel does not present 

 any ramification ; it is simply cylindrical and contractile, as de- 

 scribed by MM. Grube and Kolliker*. In these branchiae the 

 blood exhibits an alternating circulatory movement ; but this is 

 the only exception t; in all the other families the branchial 

 circulation constantly takes place in the same direction. Caecal 

 vessels with alternating circulation are met with also in the 

 tentacles of the Spiodea, Ampldctenea, and Pherusea, and in a 

 part of the so-called branchial filaments of the Cirratulea; but 

 the latter organs are not respiratory (unless perhaps lymphatic). 

 How could M. de Quatrefages commit an error so manifest 

 and so frequently repeated ? This is easily explained. The 

 branchiae are in general not cylindrical, but slightly compressed. 

 Now, in the position which they must naturally take under the 

 microscope, the artery exactly conceals the vein, and one might 



* M. Milne-Edwards, ignoring tliese observations, erroneously attributes 

 to the Tubicolous Annelida lyuiphatie branchiaj exclusively (Le9ons sur 

 I'Anat. et la Physiol, tome ii. p. 103). 



t I think I have a right to speak thus categorically. Of the twenty-six 

 families of Annelida admitted by M. de Quatrefages, 1 have studied twenty- 

 five anatomically, by the dissection of numerous species or individuals. As 

 to the twenty-sixth, that of the Hermelleu [Sabellaria), it is too nearly re- 

 lated to the Amphictenea and Terebellea to allow us to suppose that it 

 differs much from them. 



