ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 511 



on either side of the intestine. These become hollow, and separate 

 from the walls which produced them. 



The mesoderm is first formed from the inner cells of paired ecto- 

 dermic swellings. The nervous system commences with the formation 

 of cephalic ganglia on either side of the head ; the ganglia of the 

 ventral chain ajijiear as paired ectodermic thickenings. 



Madlle. (Dr.) S. Pereyaslawzewa * describes the development of 

 Caprella ferox. The ova have a transparent but very compact chorion, 

 which does not allow of the passage of much colouring matter or pre- 

 servative fluid. The nucleus, which is placed at the centre of the egg, 

 is surrounded by a thick layer of protoplasm (formative yolk), covered 

 by a layer of nutrient material, which contains a number of fat-drops. 

 After the seventh stage, the segmentation loses its regularity, and 

 becomes more and more difficult to study ; as the formation of the blasto- 

 derm is being completed, it thickens on the ventral surface along the 

 median line, while remaining more delicate elsewhere. When its for- 

 mation is completed, and it covei"S the dorsal surface of the embryo, the 

 boundaries of the cells are no longer recognizable, and the blastodermic 

 layer has the form of a mass of transparent, perfectly clear, bodies, 

 which envelope and close the yolk. As the dorsal organ is being 

 formed, a transverse groove apjDcars on the ventral surface, which 

 carries down the blastoderm into the midst of the vitelline masses ; this 

 is the commencement of the abdomen. Simultaneously two lateral 

 prominences appear above the dorsal organ ; these represent the two 

 halves of the iiead, which, therefore, are at first separate from one 

 another. The development of the body occupies fifteen days. 



In the course of the growth of the blastoderm, the constituent cells 

 divide in two directions, radial and tangential ; the thickest cells of the 

 ectoderm are found in the thickenings which go to form the extremities, 

 and in the ganglia of the ventral chain. The stomodaeum is developed 

 shortly before the rectum ; both are developed in exactly the same way 

 as in Gammarus. I'he formation of the mesoderm coincides with that 

 of the extremities ; at first its elements accumulate in the ectodermal 

 swellings which have given rise to them. In the phases which corre- 

 spond to this period of development, the mesoderm nowhere forms an 

 intermediary layer between the ecto- and endoderm. Later on, the 

 division of the mesodermic cells becomes very active, they pass the 

 boundaries of the cavities of the swellings, and become collected in 

 places where muscles will be formed. Before, however, these appear, 

 the heart begins to be developed, and as it is developed the dorsal organ 

 disappears. 



In describing the development of the endoderm and its derivates, it 

 is pointed out that the hepatic appendages are developed from endo- 

 dermal cells which form two independent tubes. 



British Amphipoda.t —In the first of his notes on British Amphipoda 

 the Kev. Dr. A. M. Norman describes a new genus and some CEdiceridae. 

 The former, which is called Megaluropus, is remarkable for the large 

 round eye which is situated en a greatly projected head-lobe, and the 

 expanded foliaceous branches of the last uropods. It appears to be 

 nearly allied to Elasmopus. The new species, 3f. agilis, has been taken 



* Bull. Soc. Imp. Nat., 1888 (1889) pp. 582-97 (2 pis.), 

 t Ann. and Mng. Nat. Hist., iii. (1889) pp. 445-60 (3 pis.), 



2 N 2 



