,. CrENOPHORA. 



j4 



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

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

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

 ausserdem durcli etwas reichlichere Muskelentwicklung und entsprechende Verdickung des Nerven- 

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

 soo-enannten Magenstiels" — which are regarded as of no importance. "Subumbrella, Velum und 

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

 zentrum, fiir die Medusen so wesentliche Charaktere, dass deren vollkommener') Mangel bei 

 Hydrocfeiia o\mfi\VQ\t&rcii jede phylogenetische Ableitung der letzteren von den Hydromedusen ablehnen 

 lasst. Es kann sich nur um eine Anahnelung, eine Konvergenzerscheinung (Pseudovelum), handeln". 

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

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

 teilende aberrante Ctenophore, ahnlich Cocln- und Ctenoplana. dar, fiir die man eine besondere Ord- 

 nung w-ird aufstellen miisseu, 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 appear to me necessary to discuss Schneider's arguments for the Ctenophoran 

 nature of Hvdroctena; 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 Ctenoplana 

 or Coeloplana. The same appHes to the Ctrnaria ctruophora of Haeckel; this latter form, however, 

 need not be discussed here anew. 



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

 Ctenoplana, viz. the Hrferoplana Newt on i of Willey (On Heteroplana, a new genus of Planarians. 

 Quart. Journ. 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 Willey 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 bod\-, otherwise nothing is known about the gastric system. "Through the whole 

 body, and especial!)- prominent in the anterior and posterior regions, is a close reticulum formed b\ 

 the anastomosis of fine moss-like tubules which probabl}- 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, estabhshed by me 

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

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



M I am ifspousible for the emphasis here. 



