INVERTEBRATA, GRYPTOGAMIA, MICROSCOPY, ETC. 577 



Gcpbyrea ; as to these latter, we find the following striking points of 

 rescmblauco between them and the Holothuroid Echinoderms : the 

 "sausage-shaped" elongated body is enclosed by a firm and naked 

 integument ; the mouth opens at the anterior and the anus at the 

 posterior pole, while in both cases the former is surrounded by a 

 circlet of tentacles ; nor is the resemblance confined to their external 

 characters, in both cases a pair of " tree-like " organs are connected 

 with the rectum of a large number of forms. Many of what are 

 now called Gephyrea the earlier zoologists jilaced, indeed, with the 

 Holothuroida, and the view that there is a close relationship is still 

 held by a number of zoologists, of whom Professor Glaus is cited by 

 our author. 



The third view is that put out by Professor Haeckcl. The 

 similarities between the Holothurian and the Gephyrean are due 

 to the action of similar external circumstances, and not to descent 

 or close genetic relation — they are not homologies, but only analo- 

 gies ; thus the tree-like organs are primitively five in the one, and 

 in-imitively two in the other group ; the arrangement of parts is 

 diyleural in the one, and pentamerous in the other ; the Echinoderms 

 are, in fine, pcntate colonies of worm-like or dipleiu-al persons, each 

 of which is comparable to a segmented worm ; the history of these 

 forms is only rendered intelligible when we regard the bilaterally 

 symmetrical larva as a nurse, and look ujjon the history of their 

 develoi^ment as involving an alternation of generation. This view 

 is supported by Sars, both father and son, by Gegenbaur, and by 

 Lange. 



To turn to the " Comet-forms " which in Professor Haeckel's 

 opinion support these views; these are those starfishes in which a 

 sejDarated arm has produced afresh the central disk and the other 

 arms. It is impossible for us to give an accoimt of the observations of 

 Martens, Kowalewsky, Sars, and Studer, but those of Sir John Daly ell 

 may well be taken as a type ; on the 10th of Jxme this observer found 

 an arm, which had evidently been lately separated from a starfish ; 

 five days afterwards four new rudimentary rays appeared on it ; ou 

 the evening of the same day (the 15th) a new mouth began to be 

 formed, and on the 18 th the animal was again completely developed, 

 save only that the four new arms were very small ; a month after- 

 wards the animal spontaneously freed itself of its original arm. 

 The true comet-form is always distinguished by one completely 

 developed arm, to which, at its central end, the newly formed disk 

 and four or five arms are connected ; at first there is no disk, and no 

 madreporic plate, while the mouth is formed by the open central end 

 of the primary arm. When the new arms have attained a certain 

 size, a small median disk appears, the mouth takes up a central position, 

 and a small madreporic plate appears on either side of the primary 

 arm. These observations lead to the following law, from which there 

 seems to be no escape. In certain Asteroida the arms break off 

 spontaneously from the disk, and each separated arm reproduces the 

 whole disk and the other arms. Further observations show that the 

 point of fissure is so placed that a small portion of the lost arm 



