748 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Platyhelminths, there are two longitudinal nerve-trunks which unite 

 posteriorly, after gradually increasing in size. The transverse com- 

 missures go directly from one trunk to the other, and often branch 

 and anastomose with their neighbours. Both the commissures and 

 the lateral nerves give off a number of fine branches ventrally. The 

 brain of Flanaria polycliroa stands at a lower level than that of D. 

 ladeum or Pol. tenuis, owing to the want of concentration of the 

 sensory nerves into anterior cerebral lobes. The eye of P. polycJiroa 

 is described as consisting of a pigment-goblet, an optic cone, and an 

 optic ganglion. The first is formed of compact pigment-granules, 

 and has its orifice directed outwards and upwards. Anteriorly to this 

 opening there is a collection of nervous substance, surrounded by a 

 number of nuclei, which appear to belong to ganglionic cells. 



The author was unable to observe the impregnation of the ovum, 

 and thinks it likely that the spermatozoa are to be found in the 

 albuminous fluid of the cocoon. Directive corpuscles were not 

 detected, probably because the ova have no investing membrane, so 

 that their presence was obscured by the contents of the cocoon. The 

 layer of fused cells, which early becomes developed, seems to be due 

 to the metamorphosis of the peripheral cleavage-spheres. The em- 

 bryonic pharynx is formed by the elongation of some of the endo- 

 dermal cells, which become converted into muscular cells, and surround 

 a central group of cells, which soon afterwards begins to make its 

 way to the surface; clefts appear in this mass and lead to the 

 gradual appearance of a lumen. This pharynx is only provisional, 

 and is at about the twentieth day replaced by the one which is 

 possessed by the adult. The author has, unfortunately, no ob- 

 servations to record on the mode of development of the excretory 

 organs, or of the finer parts of the nervous system. 



Classification of the Rotifera.* — Dr. C. T. Hudson points out 

 what seem to him to be the chief faults in the systems of Ehrenberg, 

 Dujardin, Leydig, and Bartsch, and proposes the following arrange- 

 ment of the Rotifers in well-marked and fairly natural groups. 



OEDEE I. EHIZOTA. 



Fixed forms ; foot attached, transversely wrinkled, non-retractile, 

 truncate. 



Fam. 1. Flosculabiadjb. 



Mouth central; ciliary wreath a single half-circle above the 

 mouth ; trophi uncinate. 



Fam. 2. Meliceetad^. 



Mouth lateral; wreath two marginal curves nearly surrounding 

 the head, with mouth between ; trophi malleo-ramate. 



* Quart. Journ. Micr. Sci., xxiv. (1884) pp. 335-56 (15 figs.). 



