INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 569 



that the muscular system of this animal is evidently capable of 

 enabling it to pass through the damp sand with great rapidity, as well 

 as to circle through the water with great ease. 



The mouth is triangular or T-shaped in form ; the upper lip is not, 

 as is the lower one, cleft ; both are in life capable of great power of 

 movement ; the intestinal tract appears to be somewhat complicated, 

 as is also its appendage, the proboscis ; with regard to which it is 

 pointed out that its structure is such as to enable it to bore unceasingly 

 into the sand, and so to make a passage for the more delicate hinder 

 parts of the body ; it is of a pale reddish colour. The anterior region 

 of the enteric canal is well provided with muscles, and is very firm, 

 thanks especially to the chitinous investment of its glandular layer ; 

 it has a close homology to the oesophageal region of the Nemertinea, 

 wliich it strikingly resembles in the possession of a rete mirabile ; the 

 cilia of the other form are here replaced by chitin ; a further point of 

 resemblance is to be found in its retention of irritability long after 

 death. Magelona is shown to subsist on the cast chitin of Crustacea, 

 on Foraminifera, and so on, while the ingestion of sand appears to be 

 a necessity of its existence. The blood is richly supplied with blood- 

 corpuscles of a pale red colour ; in 1852, Dr. T. Williams stated that 

 there was no species of annelid in which the true blood contained 

 morphotic elements ; but this statement, which is now shown not to 

 hold for Magelona, and has been lately shown to be untrue of the 

 earthworm, is also untrue of TereheUa (R. Wagner), Ghjcera, Phoronis, 

 and Sijllidia armata (Quatrefages), and of some Staurocephalida, 

 Cirratulida, and Opheliida (Clajjarede).* 



The ccfilom is very indistinct in the anterior region, and in it no 

 perivisceral corpuscles were to be observed ; behind the ninth segment 

 it widens out, and has, in section, a circular form ; it is divided by a 

 median ligament, and its contained clear fluid is provided with cor- 

 puscles, which are not very numerous, and vary a good deal in form. The 

 central nervous system is situated in the hypodermis, and the nerve- 

 trunks run in a very distinct neural canal. The tentacles are com- 

 pletely devoid of cilia, but thevas efferens has a remarkable contractility, 

 so that it takes the place of the cilia in respiration. Having made 

 some remarks on the generative organs, the author concludes thafc 

 Magelona has several points of affinity to Prionosjno and Heterospio, 

 and others to Spiochceiopterus ; the structural arrangements of the 

 proboscis, cephalic lobes, and circulatory organs are sui generis. 



Arrangement of the Nerve Cords in the Annelides.t— The arrange- 

 ment of the nerve cords varies so greatly in the Annelides, and a 

 knowledge of the subject is so important from many points of view, 

 that it seems well to give a separate note on this subject, the basis for 

 which is to be found in Dr. Mcintosh's paper on Magelona. 



(1) In some, the trunks lie internally to the muscles, or in a 

 ventral cleft between them ; the transverse band between the ventral 

 muscles and the hypodermis lies externally to them ; among others 



* The account of the circulatory system reappears in the ' Journ. Anat. and 

 Phys.' (Humphry) for April, 1879. 

 t Loc. Cit. 



