996 SUMMARY OF CURRENT RESEARCHES RELATING TO 



of the nucleus is so unequal that it is difficult to know whether to 

 call it " direct " nuclear division or nuclear budding. The apparent 

 absence of marked changes in the nuclear structure leads Frenzel to 

 regard it as direct. 



In a brief physiological review he notes that since the function 

 of the mid-gut gland is rather pancreatic than hepatic, the name of 

 liver is too definite. He disputes the probability of the absorption 

 of food taking place altogether within the short mid -gut, and, though 

 positive facts are not in his favour, thinks it probable that this is also 

 effected by the fore- and hind-gut. 



Development of Atyephira compressa.* — Mr. Chiyomatsu Ishi- 

 kawa has investigated the development of this fresh-water Macrurotis 

 Crustacean, which is abundant near Tokio. 



The female generative organ has the form of two elongated sacs, 

 the ducts of which arise at about the middle of their length, and open 

 to the exterior on the internal face of the basal joint of the third 

 thoracic leg. It is possible to distinguish in the ovary a germogen, 

 which has the form of a narrow transparent band, from a vitellogeu 

 in which the yolk-elements are firmest. The wall of the tube consists 

 of two sets of layers, more or less separated from each other ; blood 

 passes into these spaces and into the vitellogen, but no trace is to be 

 found in the germogen. The distribution of the blood-vessels has 

 been made out in the ovary of Panulirus. 



The youngest eggs are perfectly transparent, and measure about 

 • 01 mm. in diameter : all, or at any rate the majority of cells in the 

 pouch are destined to become eggs. The germinal vesicle is at 

 first more than one-half, but later it comes to be only one-fifth of 

 the diameter of the egg; it never has more than three germinal 

 dots. 



When the eggs are 1 mm. in diameter they pass into the vitellogen 

 to be charged with nutritive elements, and here they grow very 

 rapidly and take on a dark-green colour. The deposition of yolk 

 takes place endogenously. The protoplasm of the egg collects at two 

 points, one aroimd the nucleus and the other at the periphery ; the 

 former spreads out like rays towards the latter and unites with it. 

 The germinal vesicle disappears rapidly when the egg attains a 

 certain size. There are two covering membranes, one formed by the 

 hardening of the peripheral protoplasm of the egg, and the other by 

 the epithelial cells of the oviduct. The freshly laid egg has no 

 nucleus and is therefore a cytod. 



After describing the mode of oviposition, the author proceeds to 

 give an account of the process of segmentation ; this begins by a 

 slight notch on one side of the egg transverse to the long axis ; it 

 gradually elongates in both directions until the egg is divided into 

 two equal parts. The two halves next approach one another ; after 

 three or four hours the line becomes again uppermost, and imme- 

 diately a second line, at right angles to it, divides the egg into four 

 equal parts. When there are 256 segments, the segments at one pole 



* Quart. Jnnrn. Micr. Sci., xxv. (1885) pp. 301-428 (4 pis.). 



