608 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Coelenterata. 



Organization and Classification of the Acraspedota. *— In this 

 communication, which may, we think, be taken as a Prodrome of his 

 second volume on the Medusae, Professor Haeckel deals with this 

 division of the jelly-fishes. It is one which contains the higher forms, 

 and is in no way connected by any intermediate representatives with 

 the Craspedota. The remarkable resemblance which obtains between 

 the two divisions is due not to true phylogenetic relationship or in- 

 heritance, but to a convergence of forms or an adaj^tation to similar 

 conditions of existence. The Acraspedota and the Craspedota have, 

 according to Haeckel, arisen from two different groups of Polyps. The 

 former, without exception, possess gastric filaments and endodermal 

 gonads, and have no true velum. They arise from the Scypho-polyps, 

 or forms in which there were four interradial gastric projections 

 (tfeniolaB). On the other hand, the Craspedota have no true gastric 

 filaments, but have a true velum, and ectodermal gonads ; they arise 

 from the Hydroid Polyps, in which there are no interradial taeniolae. 

 In a phylogenetic table we see that the Hydraria [Hydra) have given 

 rise to the Scyphopolypi (Scyphostoma), and the Hydropolypi [Hi/dro- 

 stoma), and that these two phyla have always remained altogether 

 distinct from one another. 



The Discomedusfe are often regarded as representing the Acraspe- 

 dota ; but this should not be so. There are three other orders also — 

 the Stauromedusae, Peromedusae, and Cubomedusae, which three may 

 be united into the sub-legion Tesseroniae, as against the second sub- 

 legion of Ephyroniae (= Discomedusae). The Tesseridje may be re- 

 garded as the stem-group of all the Acraspedota. Of these, the 

 simplest and oldest is Tessera, which in all essential details resembles 

 a free-swimming Seyphostoma polyp. It has no marginal bodies, but 

 eight simple tentacles in their place. The closely allied Tesserantha 

 has, in addition, eight adradial tentacles, and a number of gastric 

 filaments. 



The Lucernaridae are closely allied to these " primitive and most 

 instructive " Tesserida ; they agree with them in all essential details, 

 and are only distinguished by the fact that the eight principal tentacles 

 are converted into marginal anchors or are lost, while the edge of the 

 mantle is produced into eight hollow marginal lobes or arms, each of 

 which carries a tuft of hollow tentacles. 



These two families form the orders of the Stauromedusae, which 

 are distinguished from the other three by retaining their primitive 

 simplicity, or by the absence of any special sensory organs. The 

 other three have all sensory (marginal) bodies or rhopalia, which 

 have been developed from the principal tentacles of Tessera, and con- 

 sist of a special union of an auditory and an optic organ. The Pero- 

 medusae have four interradial rhopalia, the Cubomedusae have four 

 perradial, and the Discomedusae have four perradial and four inter- 

 radial (with, in many cases, other accessory organs). 



All three orders may be easily derived from Tessera ; Pericolpa 



* Jen. Zeitsclir. f. Naturwiss., xiv. (1881) Suppl. Heft, pp. 20-9. 



