152 Descriptions of Preparations. 



which opens inside of the crown of tentacles ; whilst in the Aspido- 

 chirotae, the generative gland is made up of a single fascicle of long, 

 sometimes bifurcating, coeca, which are attached on the left side of the 

 dorsal mesentery, much nearer the oral end of the body, where they open 

 posteriorly and exteriorly to the crown of tentacles, in the dorsal inter- 

 radius opposite the medio-ventral line. The Cucumaria 2}entactes here 

 described, differs from the common Sea-Cucumber (Cucumaria commv/ais) 

 in its smaller size, smoother inter-ambulacral areae, and in not having its 

 rows of ambulacra prolonged so closely up to the anus. Internally the 

 larger of the two species differs from the smaller in having a much 

 longer intestine, more numerous generative coeca, and longer respiratory 

 trees f. 



' The two next Preparations are intended to illustrate some of the characteristics 

 of the Coelenterata as seen in the two chief classes of that sub-kingdoin, the An- 

 thozoa s. Polypi, and the Hydrozoa ; and it may be well here to give some of the 

 reasons which have induced Naturalists to accept the separation of the Echino- 

 dermata, illustrated in the last four Preparations, from those animals with which, 

 until the publication of Leuckart's views in 1848, they were classed under the 

 common name of Radiata or Zoophytes. The resemblance connoted by the name 

 Radiata has no more than a superficial basis in the organization of the Echino- 

 dermata. Not only are their radial divisions ordinarily pentamerous, whilst those 

 of the Coelenterata are ordinarily four or six or some multiple of these even 

 numbers, but they always in developmental, and usually in adult life show marks of 

 bilateral sjonmetry. The plant-like character of fixation to one spot which the 

 name Zoophyta may be taken to refer to, attaches to a very large number of 

 Coelenterata, but to only two genera of existing Echinodermata throughout life, 

 and to a third temporarily. The deposit of calcareous spicula in greater or less 

 abundance within the perisoma, and the absence of any but histological sexual 

 differences, are points common to the majority of Coelenterata and to all Echinoder- 

 mata, and both sub-kingdoms are exclusively aquatic and all but exclusively marine 

 in habit ; but these points are probably the only points of real resemblance between 

 the two subjects of comparison. The integumentary system of the Echinodermata never 

 shows any traces of the possession of the 'nettle-cells,' all but universally found in 

 Coelenterata, as also in certain Turbellarians and Nudibranchiate Mollusks, and not 

 always absent in the higher Vermes, with which the Echinodermata are probably 

 more closely connected than is usually supposed. They possess a large perivisceral 

 cavity, in which not only an intestinal tract, but two other well-defined tubular sys- 

 tems, the pseud-haemal and the water- vascular, are always, and a generative system 

 with well-differentiated outwardly opening ducts, is almost always, contained ; 

 whereas in the Coelenterata, as is shown in the next Preparation, the digestive 

 tract is directly continuous with the body-cavity, and the generative products are 

 set free from the generative glands directly by dehiscence, either into the perivisceral 

 cavity or at once into the external water. The Echinodermata are multiplied ex- 

 clusively by the intermediation of the congress of the two sexual elements ; and in 

 this absence of agamogenesis of all kinds, they contrast as strongly with the Ar- 

 thropoda and Vermes as they do with the Coelenterata ; the metamorphoses which 



