ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 957 



The interambulacral area of the buccal membrane, in the outer margin 

 of which the gills are placed, is not comj)letely covered by the lateral 

 processes of the ambulacra! plates ; it is projDosed to call the narrow 

 intermediate band the branchial area. Tliis is covered by delicate 

 calcareous plates, and not, as in the Cidaridte, by plates which are as 

 thick as those of the ambulacral rows. The central anal orifice is sur- 

 rounded by concentric circles of small calcareous plates ; the genital 

 and ocular plates are arranged in a single circle. The former are not 

 perforated by the genital pores, nor is the so-called ocular tentacle 

 always surrounded by the ocular plate. 



The remarkable vermiform movements observed by Wyville Thomson 

 in living specimens of Astlienosoma liystrix have never been explained. 

 The authors have discovered five pairs of powerful longitudinal muscles 

 running between the ambulacra and interambulacra ; these have the 

 form of broad semilunar lamellae, which consist of a number of separate 

 bundles, one or more of which take their origin from the ambulacral 

 plates. The separate cords take a radial direction, and are collected at 

 a centrum tendineum ; they may be called the musculi motores coronse ; 

 others are inserted into the buccal membrane, and may be called the 

 motores memhranse huccalis. The fibres are smooth. These muscles 

 serve also as suspenders of the enteric canal. After discussing the 

 resemblance of these muscles to the longitudinal muscles of Holothurians, 

 the authors point out the bearing of the facts on the homology of the 

 calcareous ring of Holothurians, which Johannes Miiller compared with 

 certain parts of the "lantern" of Echinoids, but which later authors 

 have rather regarded as homologous with the auricles. Their account 

 serves to support the correctness of Miiller's view. 



The organs of Stewart are well developed in Astlienosoma urens, and 

 probably also in all other Echinothurids ; as this group is regarded by 

 the authors as the oldest of Echinoids, their presence in the Cidarida 

 must be due to inheritance, and the separation of the latter as 

 Entobranchiata (Bell) from all other Echinoids must be given up. 

 Eudiments of these organs were long since found by Ludwig in the 

 Diadematidse, and the authors state that they have discovered rudiments 

 in Toxopneustes pileolus. 



The function of a renal organ is ascribed to the well-known brown 

 body which accompanies the stone-canal, and which has already had so 

 many names given to it, and so many functions ascribed to it. This 

 organ has a central cavity throughout the whole of its length, which 

 ends blindly in the immediate neighbourhood of the perioesophageal 

 ring, while it narrows towards the madreporite and becomes a fine canal, 

 which may be called the ureter. This ureter unites with the stone-canal 

 into a common collecting vesicle, which lies just beneath the madreporic 

 plate, with the canaliculi of which it is connected. These observations 

 are confirmatory of the descriptions of some recent French anatomists. 

 The walls of the central cavity are surrounded by branched glandular 

 lobes, which are themselves hollow ; all these lateral ducts open into 

 the central space. The glandular tubes themselves are imbedded in a 

 ground-substance of connective tissue ; they contain large vesicular 

 elements, which are generally arranged in several layers ; these vesicles 

 contain a nucleus surrounded by a rather fine protoplasm, which gives 

 off delicate processes in various directions ; these elements call to mind 

 the renal cells of Helicidae. Connected with the glandular lobes are 



1888. 3 T 



