512 I) It MASTERMAN ON THE FURTHER ANATOMY AND 



In this section the dorsal blood-vessel gives off an ovarian vessel running in the 

 lateral mesentery to the ovary. It appears to terminate in contact with the ovary (l.b.s.), 

 but in reality it surrounds the whole ovary, as can be easily determined in other 

 specimens. 



In fig. 13, both ovaries are seen in section at their upper ends. The ovary 

 appears to consist of a mass of typically mesodermic tissue, consisting of a fine 

 protoplasmic meshwork with nuclei scattered throughout it. Here and there are seen 

 large egg nuclei, with a deeply-staining nucleolus. With progression backwards these 

 nuclei become fewer and more prominent, whilst masses of protoplasm become aggregated 

 around them. They then (fig. 14) tend to arrange themselves in three rows, and are 

 of so large a size that they constrict the central space into a triangular lumen, which in 

 fig. 1 5 is reduced to a mere slit. 



In specimens with nearly ripe ova, the ovaries press outwards upon the rectum and 

 other surrounding parts, and as Professor M'Intosh (4) has remarked, they appear as 

 large rounded protuberances in the body of the individual. 



In the mesodermic covering of the ovary is a thin chondroid skeletal layer, which 

 becomes greatly thickened at the posterior end. 



The peculiar structure and appearance of the oviducts led them to be at first mis- 

 taken, in an external view, for eyes ; and later, when their true structure was known, 

 Dr Marcus Gunn and Professor M'Intosh (4) suggested that they were of the nature of 

 phosphorescent organs. Considering the habitat of the animal, this appears to be by 

 no means improbable, the light forming a possible attraction to the male element. It 

 seems also likely that these so-called " oviducts " function solely for the introduction of 

 the spermatozoa into the lumen of the ovary, in which fertilisation may be effected, the 

 egg being afterwards set free, possibly by the death of the parent. This is rendered 

 probable by the following considerations : — 



Firstly, the eggs ripen from the mouth of the ovary backwards, so that the most 

 advanced are found at the posterior end, furthest from the oviduct.* 



Secondly, the ripe eggs formed in the ccencecium are enormous in comparison with 

 the size of the parent, and it is difficult to conceive of their extrusion through the 

 oviducts or elsewhere without extensive rupture of the tissues. 



Thirdly, the very active asexual reproduction would justify the low sexual fecundity 

 implied in this suggestion. 



In comparing these organs with those of Phoronis, we may note that the oviducts 

 lie in a pair of lateral mesenteries, occupying a similar position to those of Phoronis, m 

 which are situated the nephridia. The ovaries are evidently proliferations of the 

 coelomic wall in each case, and the main distinction appears to consist in the " closed 

 condition of the oviducts in Cephalodiscus as compared with the " open " nephridia of 

 Phoronis, a difference very closely paralleled by that existing between the urogenital 

 systems of the Teleostei and the Elasmobranchii (compare figures 16 and 17). 



* Of. Remarks upon ovaries of Cribrella oculata, by Professor M . Sars. Fauna litt. Norvegix, Christiania, 184G. 







