DESCRIPTION OF THE PLATES. 115 



a Parietal decidua. 



b A veinous sinus passing obliquely through it by 

 a valvular opening. 



c A curling artery passing in the same direction. 



d The lining membrane of the maternal vascular 

 system, passing in from the artery and vein 

 lining the bag of the placenta, and covering e e 

 the fetal tufts, passing on to the latter by two 

 routes, first by their stems from the foetal side of 

 the cavity, and secondly by the terminal deci- 

 dual bars //from the uterine side, and from 

 one tuft to the other by the lateral bar g. 

 Throughout its whole course this membrane is 

 in contact with decidual cells, except along the 

 stems of the tufts, and the foetal side of the pla- 

 centa, where the decidual cells have degenerated 

 into fibrous or areolar fibres. All that portion 

 of the decidua which is in connection with the 

 bars, villi, and tufts, is the central or functional 

 portion of the decidua, and along with the lining 

 membrane of the maternal vascular system, or 

 external membrane of the tufts, constitutes the 

 true maternal portion of the placenta. 

 h h Two diagrams illustrating the fretal cellular 

 elements of the placental tufts. These are the 

 internal membrane, and the internal cells of the 

 tufts, and along with the loops of umbilical 

 blood-vessels constitute the true foetal portion of 

 the placenta. 



THE TESTIS AND ITS SECRETION IN THE 

 DECAPADOUS CRUSTACEANS. 



PLATE IV. Fig. 1. Figures of Entozoa from the tubuli semeniferi 

 of Orchestia littoralis, probably allied to filaria, 

 and supposed by M. Kblliker to be the sperma- 



