556 SUMMARY OF CURRENT RESEARCHES RELATING TO 



age stages are shown to be constant, definite, and " determinate," so far as 

 the formation of germ-layers is concerned. In later stages specific areas 

 of cells, known to be of definite origin, enter into the formation of par- 

 ticular organs. It is therefore prohable that the cells in cleavage stages 

 bear a definite and constant relation to future organs. A clear table of 

 the lineage is given. In an addendum, E. L. Mark and W. E. Castle 

 maintain that Lepas is a good example of modified " quartet " cleavage. 



So-called Hepatico-Pancreatic Glands of Isopods.* — L. H. Huie 

 has made some observations on the changes which these cells (in Oniscus 

 and Porcellio) undergo owing to functional activity. Their size renders 

 them a favourable subject for physiological investigations. The livers 

 are tubular glands composed of two kinds of cells in a single layer : — 

 (a) large cone-shaped cells projecting conspicuously into the lumen in 

 transverse sections of the glands ; and (b) small, more or less stellate 

 cells, inconspicuous in transverse sections. Both usually contain two 

 nuclei. The large cells contain a great quantity of yellow oil, and the 

 small cells are normally filled by minute brownish-yellow globules. 

 Fasting for not less than five days causes a diminution of the oil in the 

 large cells and the granules in the small ones, and finally the total or 

 almost total disappearance of both. The cells and nuclei shrink, the 

 oil-cavities are obliterated, and the plasm stains deeply all over, but 

 especially towards the periphery of the cell bordering the lumen. Tho 

 lumen of the livers of Oniscus is very generally infested with bacteria. 



Mysis in the Volga.t— W. Zykoff reports finding in the Volga at 

 Saratow both males and females of Mesomysis ullskyi Czern. This 

 seems to be the third case in Europe of a representative of the Mysidse 

 occurring in rivers. In 1828 Vaughan Thompson recorded Mysis 

 chamseleon and M. vulgaris from the Lee in England ; in 1875 Pengo 

 found Potamomysis pengoi Czern. in the river Udy at Charkow. Zykoff 

 has had the good fortune to add a third case, and he has for the first 

 time seen the male of this species. He regards the form as a relict from 

 the Aralo-Caspian basin. 



Annulata. 



Vascular System of Hirudinea.J — A. Oka maintains that a body- 

 cavity occurs in all Hirudinea. It is much more distinct in Glossi- 

 phonidfle and Ichthyobdellidae than inGnathobdellidaa and Herpobdellidse. 

 In the two last-named families it is much restricted by proliferation of 

 connective-tissue, &c. 



A true blood-vascular system is represented only in the Glossi- 

 phonidse and Ichthyobdeliidas. It is quite closed, and is in general 

 features comparable to that of Chaetopods. What are called blood- 

 vessels in Gnathobdellidre and Herpobdellidee are simple vessel-like 

 channels of the body-cavity. 



The IchtbyobdellidaB represent to some extent a transition between 

 the Glossiphonidse and the Gnathobdellidre, for they exhibit, besides 

 a true blood-vascular system, vessel-like lateral channels. 



* Proc. Scot. Micr. Boo., iii. (1901) pp. 85-8 (2 pis.). 



t Zool. Anzeie;., xxv. (1902) pp. 275-6. 



J Aimot. Zool. Japon., iv. (1902) pp. 49-60 (5 figs.). 



