I2 CTENOPHORA. 



radial (genital) vessels, the point from which the meridian vessels would proceed, if present, and 

 accordingly they must become quite short. 



As seen from the sections the genital organs contain a rather large cavity which is the direct 

 continuation of the genital (interradial) vessel, the branch going from the main vessel to each genital 

 organ. (PI. IV, V and VI ; the connection between the genital cavity and the main vessel is seen in 

 PI. IV, Fig. 3, the right subsagittal organ below, and likewise in PL V, Figs, n and 12). In the side- 

 walls of this cavity the genital products develop, arranged in the way typical for Ctenophorans, viz. 

 the eggs developing on the adradial side, the spermatozoa on the interradial side of the genital or- 

 gans. (Comp. PI. IV, PI. VI, Figs, i and 3, also text figures 12, p. 9). In PI. IV, Figs. 2 4, the left 

 subsagittal genital organ appears to be in contradiction to the rule; it is, however, only apparently 

 so. On following this organ through the different sections it is seen that it is really built after the 

 usual plan, only the ovary has been exceptionally developed, occupying secondarily also the greater 

 part of the interradial side, pushing the testis partly over to the adradial side, thus making some 

 disorder in the arrangement of the parts of the organ; in the Fig. 2 part of the ovary is seen in the 

 right place. In the other specimens sectioned no such disorder was found. 



The genital cavity, the homologue of the meridian vessels, is lined with a more or less vacuo- 

 lated epithelium, very similar to that of the tentacle vessels and of the ridges in the ramifying gastro- 

 vascular canals, to which it also corresponds in morphological value. It is generally very high over 

 the ovary, considerably lower over the testis. The nuclei are often arranged very beautifully in a 

 regular row near the edge of the epithelium (Comp. PI. IV, Figs. 2 4). The arrangement of the ovary 

 and the testis within the single genital organ and their relation to the genital cavity is easily tinder- 

 stood from the fig. 4 of PI. VI. It very much recalls the Fig. 3, PI. IV of Hertwig (Op. cit), which 

 represents a section through a meridional vessel of a young Beroe ; that the ovary and testis are here 

 separated both above and below, while in the quoted figure of the Tjalfiella they are close together 

 above is no essential difference; in other sections they may be separated as e. g. shown in PL VI, 

 Fig. 3, in the right genital organ. It may not be superflous to point out this close resemblance in the 

 structure of the genital organs to that of other Ctenophorans. 



The development of the genital products is partly to be followed in the sections. In PL VI, 

 Fig. 6, some larger cells are seen in the germinal zone of the ovary, with large nuclei and a very 

 conspicuous nucleolus, which stains very strongly with cosine (the sections being stained with "Wasser- 

 blau-Eosin" after Mann). These doubtless represent young eggs. In later stages they protrude into the 

 genital cavity, being surrounded by the large entodermal cells lining the genital cavity (PL VI, 

 Figs. 3 4). Whether these cells are ultimately transformed into a jelly-like mass surrounding the egg, 

 (such as occurs in other Ctenophores), when it leaves the ovary to fall into the genital cavity, I 

 cannot tell, having found no quite ripe eggs. The size of the ripe egg therefore cannot be given 

 either. The development of the spermatozoa is easily followed. The germinal zone is found at the 

 lower edge of the testis (PL VI, Fig. 4), from here the different stages of development are found gradu- 

 ally upwards (Comp. PL VI, Fig. 5 ; this figure has not been reproduced in the natural position, in 

 which the thin portion points downwards). The young spermatozoa are arranged in very conspicuous 

 packets, as described by Willey in Ctenoplana. (Also in Beroe a somewhat similar arrange- 



