ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 235 



seta, but does not pass up the whole length of the lumen. There is a 

 glandular structure amongst the nerve-endings of the great claw, which 

 resembles a salivary gland. As to the ganglion in the claw, it is not a 

 reflex centre, but is probably sensory, collecting the impressions from the 

 end-organs, and transmitting them to the central nervous system. 



The author traces out a genealogy of the setas. Starting with a primitive 

 seta, allied to a fringing seta, but not so flattened, it stood over a wide 

 canal ; the lumen was not closed; there was a single row of bristles on 

 each side, and a nerve-ending attached to its base. From this seta the 

 fringing setse were derived in one direction, and the sensory setae along 

 another line; these were at first primary tactile setsa, which became 

 modified in three directions, to give rise to auditory, olfactory, and 

 tactile setae. 



Embryology of ScMzopods.*— Herr J. Nusbaum gives a preliminary 

 sketch of the early stages in the development of Mysis CTiameleo. Before 

 segmentation begins the egg exhibits a large quantity of nutritive yolk, 

 and at the formative pole an aggregation of finely granular protoplasm 

 with a large round nucleus. A thin layer of homogeneous protoplasm 

 extends over the whole surface of the yolk. The nucleus divides and the 

 peripheral half multiplies into the nuclei of blastoderm disc, while the 

 other remains under the egg-membrane. In the middle of the disc there 

 are some large cells dividing tangentially. Some of the other cells divide 

 radially, and an accumulation of cells is gradually formed beneath the 

 blastoderm. These Nusbaum calls " vitellophagous," because they subse- 

 quently absorb the yolk-material into which they penetrate. 



The margins of the blastoderm gradually grow round the yolk. The 

 thickened disc consists of cylindrical and cubical cells, and lies on the 

 ventral surface of the posterior part of the ovum. As it widens, an un- 

 paired caudal portion, two lateral ventral strands, and the anterior head- 

 lobes gradually become differentiated. 



At the posterior cardal disc a shallow invagination is formed, and the 

 cells of the floor of the invaginated portion multiply rapidly and form a 

 solid mass of endoderm cells. The mesoderm appears as two solid strands 

 of cells, arising from the ectoderm, and lying along the thickened ventral 

 strands above referred to. They multiply rapidly and grow inwards. At 

 the time when the rudimentary limbs are appearing the mesoderm strands 

 exhibit three corresponding thickenings. Somatic and splanchnic layers 

 are afterwards differentiated. The origin of the germinal layers is com- 

 pared with that of insects, &c. The endoderm forms the paired rudiment 

 of the liver, and a portion of the midgut. On each side of the ventral 

 strand, two symmetrical, disc-like ectodermic thickenings appear at an early 

 stage. They form two oval sacs, lined by long pyramidal cells, and con- 

 taining a homogeneous substance. They represent the saddle-shaped organs 

 of Oniscus, Ligia oceanica, and the dorsal organ of Asellus and Orchestia. 



' Challenger ' Stomatopoda.f— Prof. W. K. Brooks_ thinks that the 

 primitive stomatopod was characterized by the possession of small, sub- 

 cylindrical eyes, an acutely pointed rostrum, a smooth hind-body, a short 

 wide smooth carapace, very small antennary scales and uropods, and a telson 

 which was wider than long. This primitive form is represented to-day by 

 Protosquilla, from which the various genera have diverged. Most near to 

 it stand Gonodactylus, Pseudosquilla, and Coronida; the last leads to 

 Lysiosquilla and Squilla. 



* Biol. Centralbl., vi. (1887) pp. 663-7. 



t Keport of the Voyage of H.M.S. ' Challenger,' Monograph xlv., 4to, London, 

 1886, 116 pp. and 16 pis. 



R 2 



