232 SUMMARY OF CURRENT RESEARCHES RELATING TO 



very early into the endoderm, where they become differentiated into 

 germ-cells as Weismann had supposed. 



Cunoctantha and Gastrodes.* — Prof. A. Korotneff has notes on these 

 two difficult forms ; Gastrodes is new ; of Cunoctantha he has studied 

 two quite young stages which he found in the stomach of very young 

 Geryonise, where they appeared as small white dots. A transverse section 

 through the gastric wall of a young Geryonia revealed an elongated oval 

 larva completely imbedded in an endoderm formed of large cells. Its 

 ectoderm consists of long delicate cells, which only form one row, and 

 contain a considerable number of nematocysts. These ectodermal 

 elements are, obviously, in a state of active division, at the free pole of 

 the body, and the appearance was that of a somewhat coarsely granular 

 Plasmodium, in which separate nuclei were imbedded. At the free pole 

 the ectoderm and entoderm pass into one another ; the larva under 

 observation was just forming its endoderm, and only two nuclei were 

 apparent in that layer. In a later stage the ectoderm was found to 

 contain a considerably larger number of nematocysts, and the endoderm, 

 though still plasmodial in character, had many more nuclei, which were 

 much smaller than those of the ectoderm. One nucleus of the ingrowing 

 ectoderm has become very large, and is placed at the upper, oral end of 

 the larva ; this is, no doubt, the peculiar colossal nucleus of tlie larva. 

 The nematocysts, which are wanting in the adult Cunoctanthse, are 

 present in numbers in free-swimming larvae. The loss of these organs 

 may be due to the acquirement of a parasitic habit. 



The name of Gastrodes parasiticum is given to a form which appears 

 to have some affinities to Cunoctantha ; it was found in the gelatinous coat 

 of Salpa fusiformis in the winter of 1886; in 1887 the author failed to 

 find it. When slightly magnified it has the form of a round cake with 

 a flat base and a curved upper surface. From the base a process projects 

 into the interior ; looked at from above this invagination is seen to carry 

 a central oral opening. It is a scarcely altered gastrula, for it is a 

 saccular organism in which only two layers can be made out, which 

 has no true coelom, and takes in nourishment by means of a primitive 

 mouth. This mouth is not at the end of the body, but at the tip of a 

 proboscis-like prolongation which is invaginated into the interior. It 

 calls to mind the stomach of an Actinian, and leads into a cavity which 

 has, however, no septa. The ectoderm and endoderm are separated by 

 a supporting lamella. The ectoderm is of the simplest construction 

 on its curved surface, for there is there a single layer formed of low cells, 

 and only in places multilaminate ; this layer owes the simplicity of its 

 structure to the parasitic habit of Gastrodes ; there are no nematocysts 

 or muscular fibres. On the lower surface and on the oral tube there are 

 large distinct ovarian cells, in which may be seen a large germinal vesicle 

 and a fine reticulum ; they form an unbroken series round the margin of 

 the animal ; the complete development of these eggs may be studied in 

 one and the same individual. The gelatinous layer is a thin lamella 

 which is only well developed at the margin, where it forms a ring. The 

 endoderm consists of two sets of elements ; some are low, cubical cells 

 like those of the ectoderm, others, which are large, form the lateral walls 

 of the gastric cavity ; the latter also form a plasmatic network. There 

 are no special gland-cells in the endoderm of Gastrodes. 



* Zeitschr. f. Wiss. Zool., xlvli. (1888) pp. (J50-7 (1 pi.). 



