CTENOPHORA. 

 34 



Ctenophorenschhmd", because their histological structure is not in accordance with that generally- 

 found in the Hydromedusae, while they more resemble what obtains in Ctenophores. The resemblances 

 to Hydromedusge are thus restricted to "die velumartige Einkriimnung des unteren Korperrandes, der 

 ausserdem durch etwas reichlichere Muskelentwicklung und entsprechende Verdickung des Nerven- 

 systems zu einem inneren Ringnerven ausgezeichnet ist, und ferner auf die Anwesenheit eines kurzen 

 sogenannten Magenstiels" — which are regarded as of no importance. "Suburabrella, Velum und 

 ausserer Velumrand sind in ihrer bekannten Ausbildung, als Bewegungsorgan und Sinnes- 

 zentruni, fiir die Medusen so wesentliche Charaktere, dass deren vollkommener ■) Mangel bei 

 I/ydroclenaohneweitexes jede phylogenetische Ableitung der letzteren von den Hydroraedusen ablehnen 

 liisst. Es kann sich nur uni eine Anahnelung, eine Konvergenzerscheinung (Pseudovelum), handeln". 

 Ilydroctena is thus "einzig und allein an die Ctenophoren, in keiner Weise aber an die Cnidarier, an- 

 zuschliessen. Sie stellt eine merkwiirdige, zweifellos jugendliche, daher besonders schwierig zu beur- 

 teilende aberrante Ctenophore, ahnlich Coelo- und Cfriioplana," dar, fiir die man eine besondere Ord- 

 nung wird aufstellen miissen, ohne dass aber die Notwendigkeit erwachst, auf Grund des Mangels von 

 Ruderplattchen eine ganz neue Klasse einzurichten. Fiir die Erkenntnis der verwandtschaftlichen 

 Beziehungen der Ctenophoren zu den Turbellarien erscheint Hydroctena zurzeit bedeutungslos". 



It does not apj^ear to me necessary to discuss Schneider's arguments for the Ctenophoran 

 nature of H}'droctena; his whole reasoning appears rather too much influenced by the preconceived 

 idea that Hydroctena should be a Ctenophore. I would only point out that it seems, in the present 

 state of knowledge, unjustifiable to lay so much stress on .some points in the histological structure as 

 is done here, while at the same time another important histological fact (the cnidoblasts) is regarded 

 as of no importance. Schneider has, in fact, produced no additional evidence for the Ctenophoran 

 character of Hydroctena. — To Tjalfiella it has no relation whatever, and no more to Cfeiwplaiia 

 or Coeloplana. The same applies to the Cteiiaria cteiiopliofa of Haeckel; this latter form, however, 

 need not be discussed here anew. 



One form nmst still be mentioned, which has been maintained as a relative of Coeloplana and 

 Ctenoplana, viz. the Heteroplana A'ctcAw/ of Willey (On Heteroplana, a new genus of Planarians. 

 Quart. Jomn. Micr. Sc. N. S. 40. 1898. p. 203). I confess that I am quite unable to see in the description 

 of this animal given by Wille>- the slightest reason for associating it with Coeloplana and Cteno- 

 plana. The anatomy is very- incompletely known; it is stated, however, that there is a cerebral 

 ganglion and a large number of marginal eyes. On the other hand, there are no tentacles and no 

 apical organ; there are some branching intestinal canals and the mouth is placed in the middle of 

 the length of the body, otherwise nothing is known about the gastric system. "Through the whole 

 body, and especiallv prominent in the anterior and posterior regions, is a close reticulum formed b\ 

 the anastomosis of fine moss-like tubules which probably constitute the genital apparatus". — That 

 there is here not the slightest indication of a Ctenophoran nature I think will be universally agreed. 

 In spite of the anatomical structure, however, Willey states that "on account of its remarkable 

 relations of symmetry I (he) should place this genus in the order Archiplanoidea, established by me 

 (Willey) for the reception of Coeloplana and Ctcnoplana, because ... it would appear to be more 

 nearly related to a biradial than to a bilateral t\pc like the Planarians. This seems to follow from a 



') I am responsible for ihc empluisis here. 



