ZOOLOGZ AND BOTANY, MICEOSCOPYj ETC. 87 



parent bodies appeared, which seemed to settle upon the Melicerfa as it 

 swayed backwards and forwards in its uncovered state. The next day the 

 Melicerta was very lively, and was busy repairing its tube, as if nothing 

 had happened. 



New Parasitic Cymothoid.* — M. Z. Fiszer describes a new Cymothoid 

 genus parasitic in the fresh-water fish Idus WalecMi (Dyb.) = Cijpricus 

 lacnstris (Pall.). In structure it resembles Livoneca sinuata (Eochet) ; while 

 in mode of life it approaches the Isopods, and especially Butoniscus. It is 

 a true parasite, not a commensal. 



Vermes. 



Origin of Annelids from the Larva of Lopadorhynchus.-j- — Herr N. 



Kleinenberg devotes the first chapter of his essay to observations on the 

 germinal layers, in which he gives a critical account of the investigations 

 on this subject. He is himself of opinion that mature Coelenterates have 

 no mesoderm, and that the median germinal layer of embryos of higher 

 Metazoa is a mere conventional idea, which does not correspond to the fact. 

 What has hitherto been called the mesoderm is either the sum of inde- 

 pendent heterogeneous rudiments which arise within the primary germinal 

 layer, or is a single rudiment of a definite tissue or of organs which 

 eventually undergoes partial metamorphosis. As a rule, well-marked ecto- 

 dermal muscle-rudiments and paired appendages of the archenteron are 

 regarded as part of the median germinal layer. In every case the homology 

 of organs must be established by their genetic relations to the two layers 

 of the coelenterate body. These layers give rise to special tissues which 

 have no power of producing fresh tissues, and, on the other hand, the 

 tissues and organs which arise directly from one of these layers are able 

 to bring forth other tissues and organs ; in no living part of the body is 

 the internal force of metamorphosis completely lost. The genetic relation 

 between any given organ and the primary germinal layer is not lost; it is 

 only separated by the intercalation of one or more intermediate stages ; 

 none of these intermediate stages are represented by an indifferent germinal 

 layer, but always by a tissue or organ with a specific activity. Thus, the 

 permanent peritoneal investment of the enteron of LopadorhyncJius does 

 not arise directly from the ectoderm, and still less from any other germinal 

 layer, but from the metamorphosis of part of a quite specific rudimentary 

 tissue — the muscular layer. The peritoneal epithelium consists of altered 

 muscle-celLs, and as the muscle-plates arise directly from the ectoderm, the 

 latter are secondary and the former tertiary descendants of the ectoderm. 



This mode of regarding the subject appears to open out a further field 

 for embryological investigations ; where an organ does not arise directly 

 from a germinal layer, the nature of the permanent or temporary inter- 

 mediate organ must first be settled, and in the second place we must 

 investigate how far this genetic series is constant within one or more 

 classes of animals. The removal of the mesoderm frees embryology of an 

 embryonic constituent. 



The second chapter deals with the development of the external body 

 form of LopadorhyncJius, which is described in detail ; the youngest larvjB 

 found had an almost spherical form, which is divided into two equal halves 

 by a completely closed circlet of cilia ; the upper may be called the 

 umbrella, the lower the subumbrella. Both ectoderm and endoderm are 

 rather thick, and the latter incloses a spacious archenteric cavity. Largo 



* Kosmoa 

 t Zoitschr 



(Polish^ 1SS5, p. 458. Cf. Arch. Slav, de Biol., i. (1SS6) p. 466. 

 . f. Wiss. Zool., xliv. (1SS6) pp. 1-22S (16 pis.). 



