67 



studied with regard lo its devolopinenl. It is to be sincerely hoped that 

 some Australian naliiialist will take up this matter for a conijilete study, 

 which will need a rich snp|)ly of material and also constant access to 

 living material. 



Fertilization was undertaken on Fehr. 25lh H)15. The development 

 proceeded at no e.\ee|)ti()nal speed; the gastrulation took place at the 

 age of ca. 18 hours, while the first metamor|)hosed specimens were found 

 after 4 — 5 days. The eggs are large, ca. 0.5 mm, red-yellowish and quite 

 opaque. They float at the surface of the water; this is the case 

 also in PluiUacdnlhus ixin'ispiniis. while il is olluMwise unknown in lu'hi- 

 noids. II is evideiilly due lo tiu' fad tiial liie egg contains some fatty 

 substance; though I did not observe this in the living objects, it is easily 

 seen in the ])reseive(l eggs liiat they have a vacuolated structure, and 

 it can hardly be doubled that these vacuoles musl contain some fatly 

 substance which nuikes the eggs lighter than the water. The same vacuol- 

 ated structure was found in Phyllacanlhus parvispinus (p. 24 — 25). 



The cleavage is total and perfectly regular. It appears that the blastula 

 is not folded, as is the case in Phijllacanthus. The formation of the mesen- 

 chyme could not be followed in detail. It is seen to begin very early; 

 in the stage represented in PI. XVIIl. Fig. 1. which is (i hours old and 

 apparently either in the .'52- and the 64-cells stage (this cannot be definitely 

 ascertained from the sections), one cell is seen lying in the middle of the 

 blastocoel cavity, which musl. evidently, be a mesenchyme cell. Fl. XVIII 

 Fig. 2, representing an 1<S hours old blastula, shows the blastocoel cavity 

 completely filled up by vacuolated mesenchyme cells; Ihey are still un- 

 difTerentiated and of the same general aspect as the ectoderm cells, which 

 latter do not yet form a regular epithelial layer. The whole of the embryo 

 is full of large and small vacuoles, which must, evidently, undergo 

 divisions together wilh the cells, as is apparent from the fact that they 

 are much more numerous and, upon the whole, smaller in the older than 

 in the younger stages. (Comp. PI. XVIII, Figs. 1 — 2.) 



A further advanced stage, from a culture 18 hours old, is shown in 

 PI. XVIII, Fig. .3, representing the fully formed blastula. The ectoderm is 

 now a typical, higii epilheliuni, slightly highei- in one side, where the 

 gastrula-invagiualion is to take place. The meseucluMue has undergone 

 a noticeable dilTerentiation. the cells forming now merely a fine reticulum 

 between the vacuoles, which have partly united into some very large 

 ones. Some few vacuoles are still found in the ectoderm. This peculiar 

 structure of the mesenchyme, recalling a parenchymatous plant tissue, 

 is retained during the whole process of the embryonal development, 

 until the metamorphosis has been completed. 



9» 



