366 The Structure of the Annelids. 



not presenting any appreciable structure. ...... At the 



close of a variable time the branchiae contract, although 

 no muscular fibres can be distinguished. The ampullae empty 

 themselves, and sometimes completely disappear. The blood 

 runs by the central canal of the branchiae, and arriving at the 

 base of that organ, passes into the efferent vessel. In this 

 return movement it necessarily meets with the venous blood, 

 and must mix with, a certain quantity of blood which has 

 not been subjected to the action of air." Bearing in mind 

 this radically false description, let us see how the normal 

 circulation takes place in the branchiae of an Annelid. 

 There cannot ordinarily be any mixture of arterial and 

 venous blood. In fact, the artery goes to the extremity of 

 the branchia, where it turns upon itself to return as a vein. 

 Vein and artery are exactly parallel to each other. Through- 

 out the whole length of the branchia these two vessels are 

 placed in communication by a double series of vascular loops, 

 Avhich pass into the subcuticular layer, and which offers the 

 greatest facility for the action of water charged with oxygen, 

 through the very thin cuticle. As for the contractility of the 

 pretended ampulla?, there is nothing of the sort. Certain 

 genera, like the Terebellians and Telethusians, for example, 

 exhibit many rythmical contractions all through the branchia, 

 but not of the vessels themselves. Moreover, this fact is 

 exceptional. In the family of the Serpulse only do the 

 branchiae exhibit even a remote resemblance to the descrip- 

 tion of M. de Quatrefages. In fact, in these Annelids the 

 artery is continued directly into the vein at the base of the 

 branchiae, and from this point of reunion a single vessel pro- 

 ceeds, which penetrates the branchiae, and sends a caecum, into 

 each branchial branch. But M. Quatrefages describes in the 

 secondary branches of the branchiae of the Serpulians an 

 apparatus of ampullae, of which no trace exists. The blind- 

 vessel exhibits no ramification, it is simply cylindrical and 

 contractile, as described by Grube and Kolliker. In their 

 branchiae, the blood exhibits an alternating movement, which is 

 exceptional. In all the other families the branchial circulation 

 is continuous in one direction. Blind vessels with alternating 

 circulation, are found in the tentacles of Spiodians, Amphi- 

 ctenians, and Phcrusians ; in one part of the so-called branchial 

 threads of Cirratulians, but these organs are not respiratory 

 (unless, perhaps, lymphatic). [M. Claparede then remarks on 

 the way in which M. Quatrefages was misled, and observes 

 that the point was cleared up thirty years ago by Grube.] 



" Reproductive Apparatus. — The reproductive apparatus of 

 Annelids remains very imperfectly known. It is true 

 numerous works have thrown fresh light upon the educatory 



