Angular Sea-Cucumber. 153 



For the danger which, owing to the habits of the Holothurioidea 

 of ejecting their viscera when alarmed, may attend upon the 

 basing of specific or other differences upon the presence or 

 absence of the internal organs, see Forbes, History of British 



they do go through differing essentially from the phenomena known as 'alternation 

 of generations,' in that a part, and usually a large part, of the larval organism, ia 

 worked up into the composition of the sexually perfect individual. While the 

 characters of the Coelenterata are such as to make them into a sub-kingdom with 

 more sharply circumscribed boundaries than those of any other, except the Verte- 

 brate sub -kingdom, it must be confessed that the characters of the Echinodermata, 

 as presented to us not only in their life-history but also in their structure, ap- 

 proximate them so closely and at so many points to the sub-kingdom Vermes, as to 

 tlirow some doubt upon the propriety of separating them, as has been done here, 

 and as is all but universally done by foreign Naturalists, from the Vermes, and 

 elevating them to the rank of a separate and co-ordinate sub-kingdom. For viewing 

 the Echinodermata as a sub-kingdom co-ordinate with the sub-kingdoms Arthropoda 

 or Vermes the following justification may be offered. No Echinoderm ever presents 

 any trace of transverse, as opposed to antero-posterior segmentation of its body, 

 unless the jointed character of the peduncle of the Crinoidea constitutes a real ex- 

 ception to this rule ; whilst the perhaps most nearly allied order (or class?) of Vermes, 

 the Gephyrei, do occasionally, Fhascolosoma Cumanense, Keferstein (Zeitschrift fiir 

 Wiss. Zoologie, xvii. , 1867, p. 53), show rudiments of the same division of the body 

 into transverse compartments, which we have so well marked in the typical Annelids. 

 They never multiply except through gamogenesis ; gemmation, to the existence 

 of which, actually or potentially, the presence of the transverse compartments just 

 mentioned may be considered to speak, being as entirely unknown in them as is 

 parthenogenesis, whilst both forms of genesis are common in Vermes. The rarity 

 of hermaphroditism amongst the Echinodermata, and the non-existence in them 

 of any sexual differences except those of the ultimate histological structure of the 

 respective sexual glands, are minor points of difference between the two groups 

 of animals under comparison. Their possession in common of the power of repairing 

 great mutilations and injuries, as also of maturing sexual products before attaining 

 their full size, may be connected probably vdth their common aquatic habit, and 

 may be considered as constituting a point of physiological rather than of moqiho- 

 loi^ical affinity. 



On the other hand, there can be no doubt that the Echinodermata as a whole 

 present, both in their life-history and in thcu- anatomical structure, many points 

 of affinity, firstly, to the Vermes as a whole, and secondly, to each of the four great 

 orders into which they are here divided. The passing through a larval stage, in 

 which locomotion is effected by zones or circlets of cilia, is common to the majority 

 of Vermes and to almost every Echinoderm ; and the clothing of the interior of the 

 perivisceral cavity and of the digestive tract with the same microscopic element 

 is a second point common to the majority of Vermes and to all known Echinodermata. 

 Tliirdly, all Echinodermata and almost all Vermes possess a system of vessels, which 

 in either may be either locomotor or depuratory in function, but which are distinct 

 from the cavities in which the true blood is lodged, though they may communicate 



