598 SUMMARY OF CURRENT RESEARCHES RELATING TO 



tion revealed the nucleus not at tho periphery, but in a mass of pro- 

 toplasm in tho centre of the ovum ; from this mass amoeba-liko 

 processes radiate in all directions, and form a protoplasmic network 

 throughout the egg ; the nucleus is no longer a distinct vesicle. 

 Early on the second day the nucleus and the central mass of proto- 

 plasm divide into two parts, but the parts remain connectod by a 

 network of protoplasm. At the close of segmentation there are a 

 number of masses, each with a dense central portion in which is the 

 nucleus, while the outer portion is broken up into innumerable 

 processes, Avhich cement the masses together and permeate the yolk 

 in every direction. 



Mr. llcathcote attaches more importance to the connection of 

 layer with layer by means of cell-processes than to the connection of 

 cell with cell. He believes that nothing of the sort has been de- 

 scribed before, but more than ten years ago Prof. Ray Lankester 

 (in vol. xiv. Q. J. M. S.) directed attention to " an important histo- 

 logical arrangement seen " in a specimen of a developing Lymnseus, 

 where there was " a connection of tho endodermal mass of cells with 

 those forming the body-wall by means of long processes . . . the 

 processes appear to be actual filaments of the cell- substance of the 

 endodermal cells." The mesodermal " keel " is formed both by 

 ectoderm and endoderm ; later on, the greater part of the mesoderm 

 becomes arranged in two parallel longitudinal bands along the ventral 

 surface of the embryo, and these bands are connected by a thin 

 bilaminate portion; the mesodermal somites are at first solid, 

 but later a cavity appears in them ; the formation of the meso- 

 derm almost exactly resembles that of spiders, as described by 

 Balfour. 



The nerve-cords are, at an early stage, widely separated from one 

 another, but connected by a thin median portion ; later on, they 

 almost form one cord. The lumen of the Malpighian tubes is from 

 the first continuous with that of the proctodeum. The author 

 concludes by comparing his results with those of earlier observers ou 

 this and allied forms. 



y. Prototracheata. 



Development of the Cape Species of Peripatus. * — Mr. A. 

 Sedgwick enters into fuller details as to the development of Peripatus 

 than in his communication to the Eoyal Society which we have 

 already noticed.j Notwithstanding the sponge-like structure of the 

 ovum of P. capensis it can hardly be doubted that some not very 

 remote ancestor must have had an ovum heavily charged with food- 

 yolk ; in P. novse zealandise the ovum is considerably larger 

 (1*5 x 1 mm.) than that of P. capensis, and contains a largo amount 

 of food-yolk, while the shell is thick and chitinous. On the other 

 hand, the West Indian species described by Kennel has a small ovum 

 (0 - 04 mm.); so that we have in P. novse zealandise with greatest 



* Quart. Journ. Micr. Sci., xxvi. (18S6) pp. 175-212 (3 pis.), 

 j- See this Journal, ante, p. 239. 



