ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 429 



median region of the body there are four other suckers, which are often 

 of a bright red colour. The excretory pore at the hinder end of the 

 body is the orifice of a single duct, which is not swollen into a vesicle, 

 and which soon divides into two. The two branches extend to the base 

 of the anterior sucker, where they bend backwards to pass into the 

 general parenchyma of the body, where they terminate in small swollen 

 ends, which are, in all probability, vibratile infundibula. There are 

 calcareous grains in the parenchyma of the body. As the forms ex- 

 amined were devoid of generative organs, it is probable that they are 

 immature, and that they are destined for some large fish or a Cetacean. 

 The Cestode parasites of Sepiola atlantica and Pleurobracliia pileus are 

 distinguished from that here described by the absence of the enormous 

 anterior sucker. The Planaria of the Solen is never more than two 

 millimetres in length ; the body is clothed in cilia which take on special 

 characters near the anterior end. Two large black eyes, provided with 

 a very large crystalline lens, are situated at about the level of the mouth, 

 and receive large nerves from the cerebral ganglia. The mouth is sur- 

 rounded by a rosette, and followed by a distinct, simple, and elongated 

 digestive tube. Beneath the peripheral cellular layer which carries the 

 cilia, there is a dense, pale yellow parenchymatous layer, while the rest 

 of the body is filled by a colourless vesicular parenchyma ; in this last 

 tissue ova are found in all stages of development, and the young are 

 not exjielled until they are completely developed. Vesicles filled with 

 spermatozoa are found in the same parenchyma. On either side of the 

 body there are elongated tracts, which appear to be accessory glands of 

 the reproductive apparatus. 



Echinodermata. 



Longitudinal Muscles and Stewart's Organ in Echinothurids.* — 

 Herren P. and F. Sarasin have made some anatomical investigations on 

 the Echinothurid which they called Cyanosoma urens, but which they 

 now recognize to belong to the genus Asthenosoma. The five pairs of 

 longitudinal muscles which extend between the boundaries of the 

 ambulacra and interambulacra are not simple smooth bands, but are made 

 up of a number of radially arranged muscular bundles. The separate 

 bundles arise from the outermost ends of the ambulacral plates, and 

 extend centrally into a small tendon. The tendons fuse with one another, 

 and so form a true centrum tendineum about the middle of each muscle. 

 A complete muscle, seen from the side, is semilunar in form ; its lower- 

 most bundles are inserted into the auricles ; from the adoral auricular 

 surfaces there arise still wider, but much weaker bundles, which are 

 inserted serially into the buccal membrane. These semilunar longi- 

 tudinal muscles divide the body-cavity into ten chamberlets, of which the 

 five interambulacral are broader than the five ambulacral. Sir W. 

 Thomson saw these muscles, but described them as mere fasciae ; they 

 not only serve as locomotor organs, but also as suspendors of the enteron. 

 Such muscles are wanting in Echinids with firm tests, but in the Dia- 

 dematidae and allied forms the relations of the enteric mesentery recall 

 the arrangement of muscles in the Echinothuridaa. The organs of Stewart 

 were first seen in the Cidaridas ; in Asthenosoma they are also well 

 developed ; they are five thin-walled vesicles, about five centimetres 



* Zool. Anzcig., xi. (1S8S) pp. 115-7. 



