296 Miscellaneous. 



protoplasm, travel towards the surface, and a uniform blastoderm is 

 finally constituted *. 



^ The rudiment of the future germinal streak now becomes recog- 

 nizable on the ventral surface of the ovum in the shape of a thick- 

 ening of the blastoderm, and three separate thickenings may be 

 remarked in the extent of this rudiment; these are the paired 

 anterior optic lobos and an unpaired posterior thickening, which 

 gives rise by the process of multiplication to a large number of cells 

 (meso-endodcrm). This internal mass of cells becomes further 

 differentiated into three rudiments: — (1) The yolk-cells, which 

 migrate into the yolk, (2) the endoderm- and (;3) the mesoderm- 

 cclls. 



The proctodfEum is formed earlier than the rudiment of the 

 stomod;eum and has the appearance of a very long tube. Both of 

 these structures originate as invaginations of the ectoderm. The 

 mid-gut is built up from the cell-material of the endoderm. As 

 the cells of the endoderm multiply they arrange themselves so as to 

 form an epithelium. The liver develops very early on the ventral 

 surface of the endodermal furrow, and forms in the anterior portion 

 of the latter two lateral tubes, which are composed of large cells. 

 These rudiments are paired and present the appearance of folds, 

 which are open upon the dorsal side ; their edges grow together, 

 and two hepatic sacs are formed from them, each of which becomes 

 divided into t\vo secondary hepatic sacs in consequence of a longi- 

 tudinal invagination. 



The entire central nervous system originates as a thickening of 

 the ectoderm at the period of the formation of the anterior ap])en- 

 dages. _ In the early stages it takes the shape of paired ectodermal 

 thickenings ; these gradually coalesce and give rise to an unpaired 

 cord, from which the 18-19 ganglia are subscquentlv formed. 



The unpaijed eye develops from two separate thickenings of the 

 hypodermis of the foremost optic lobes, and undergoes a complicated 

 metamorphosis. 



The earliest rudiment of the heart takes the shape of a compact 

 collection of mesoderm-cells on the dorsal side, in which the cavity 

 subsequently appears. 



The genital organs also develop at the same time ; these apjicar as 

 a paired mesodermal rudiment situated above the intestinal canal. 



The dorsal organ arises very early on the dorsal side as an oval 

 aggregation of ectoderm-cells ; it persists for a long time, and 

 disappears after all the organs of the animal are formed. 



A complete memoir of mine ujion the embryology of the Cumacca, 

 accom]Kinied by three plates, will be publisjicd in tlie • Memoires de 

 la Societe des Xaturalistes dc la Nouvelle-liussie a Odessa.' — Zooh- 

 (jmhcr Anzei</tr, xvi. Jahrg., no. 4;50, October 2, 1893, pp. 38G, 387. 



* I observed this in r(iraj)0(loj)si)!: cormifd and Gchia Ittorali'j. 



