26 THE VOYAGE OF H.M.S. CHALLENGER. 



preservation allowed of a detailed histological examination, which on the one hand con- 

 firmed the view already put forward as to the endodermal origin of the reproductive organs, 

 and on the other threw new light on the nature of the filamental apparatus. 



The youngest ovicells are placed on the margins of the ovary, especially on the lower 

 and upper ; they were unmistakably recognisable as ova from the size of 9 m upwards, and 

 then consisted almost entirely of the nucleus, surrounded by a thin mantle of protoplasm. 

 They lie between the bases of the epithelial cells, distinctly still outside the supporting 

 lamella, often united in small groups. So far Corallimorjihus confirmed what had 

 already been observed in Calliactis {Sagartia) parasitica (Actinien, p. 88); but, on the 

 other hand, it was a new condition, that relatively large ova, measuring from 40-50 fi in 

 longitudinal diameter, were still found in the endoderm ; since they were almost as long 

 as the epithelial cells, one end reached nearly as far as the surface. Twice I observed one 

 of these larger cells, which was clearly in the act of migrating into the mesoderm (figs. 2 

 and 3). It had an amoeboid, hour-glass-shaped, constricted body, of which one end lay 

 in the epithelium, the other in the mesoderm ; the nucleus was mostly in the latter, but 

 the point of it projected into the former. 



The ovicells enclosed in the mesoderm all appeared to me to have, from the first, the 

 filamental apparatus, though in difi"erent stages of development. In the largest, almost 

 mature ovicells (fig. 7), it is a conical body, whose base rests on the surface of the ovum. 

 It likewise lies in the mesoderm, and its extreme point only reaches to the base of the 

 epithelium : in this way it is distinguished from the formation of the same name in 

 Calliactis, which belongs to the epithelium itself, and even projects as far as its upper 

 surface. The distinction is of no importance, and is clearly owing to the different 

 development of the connective tissue, which is very visible in CoralUmorphus, whilst 

 in Calliactis it is so scanty that the ovicells lie close to one another, and only a delicate 

 supporting framework remains when they are taken away. 



A second diSerence is of greater importance. In Calliactis it was not possible to dis- 

 tinguish nuclei in the filamental apparatus, which thus showed itself to be a differentiation 

 of the ovum itself, whilst its cellular structure is very distinct in CoralUmorphus. The 

 apparatus consists of filament-shaped cells, carrying their nuclei on the base resting on 

 the ovicell. Preparations stained with carmine showed us hei-e a corona of oval bodies 

 coloured red. It is possible that, in spite of all trouble taken, I did not succeed in find- 

 ing out the nuclei in Calliactis, because I was working with osmium preparations, in 

 which the nuclei often are difficult to colour. I might, however, have had to deal with 

 diff'erent stages of differentiation of the structure, and this is corroborated l^y the 

 following observations on the development of the apparatus in CoralUmorphus. 



Young ovicells have a single finely striated process, piercing the supporting lamella, by 

 which they are fastened on the base of the epithelium. The epithelium is modified in a 

 peculiar fashion at the point in question ; whilst it is elsewhere overloaded with roundish 



