ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 961 



When the last sign of the central yolk disappears the embryo under- 

 goes histolysis, the cell-walls disappearing, and the plasmatic bodies 

 uniting ; the nuclei are completely filled with highly refractive chromatin, 

 and pass to the centre of the body, where they unite to form the so-called 

 embryonic granular masses. 



The syncytial plasma becomes differentiated into two layers ; the inner 

 one has in its centre the nuclear masses. In this condition the eggs pass 

 out with the ffeces of their host, and make their way into the intestine of 

 the larva of Cetonia aurata. 



The embryos, by the aid of their boring apparatus, bore through the 

 chitinous lining of the lumen of the intestine, and through the glandular 

 into the subjacent muscular layers. The free and exceedingly agile 

 embryo has the form of a wide flask with a spherical base; besides the 

 numerous small spines, which thickly cover the whole body, it has five 

 large hooks, which are placed at the anterior end, and can be withdrawn 

 into it. In their resting-place the embryos increase considerably in size ; 

 the first change which becomes apparent is that six nuclei become set free 

 from the anterior end of the central nuclear mass ; these become surrounded 

 by a common plasmatic mass, which gradually assumes the form of an 

 equilateral cone. On each of the six nuclei a small hook appears, in which 

 it is not difiQcult to recognize the spinous process of the definite holding 

 organ ; when they have attained a certain size they pass forwards, and six 

 fresh hooks appear ; this process is repeated for from five to seven times. 

 Almost simultaneously with the proboscis the rudiment of the body-covering 

 of the definite worm is laid down in the form of a large-vesicled syncytium. 

 In the anterior region the nuclei are laid down in two parallel zones. 

 When the larva is from 4-5 mm. long the chief syncytium becomes con- 

 verted into a simple layer of high cylindrical cells. The latter secrete a 

 colourless mass, which later on hardens into the fibrous tissue of the sub- 

 cuticula. But before this haj^pens the first primitive muscle-fibres appear 

 in the vertical walls of the cylindrical cells ; these increase in number very 

 rapidly ; they break through the outer limiting membrane of the cells, and 

 make their way into the still soft fibrous tissue of the subcuticula. 



The endoderm gives rise to the body-musculature, the gonads, and the 

 efferent genital ducts; the syncytial origin of the first of these is 

 described. 



y. Platyhelminthes. 



Developmental Cycle of Taenia nana.* — Prof. B. Grassi, in commencing 

 his observations on the developmental history of Tsenia nana, believed that 

 the intermediate host of this human parasite was the mealworm. But all 

 the experiments which he made were useless, as were also those made on 

 animals, such as edible molluscs, lice, and so on, with which man comes 

 into contact. The suggestion then recommended itself that, neither with 

 this worm nor with T. murina was there an intermediate host at all. Trying 

 this with young white mice, and carefully looking to their food after having 

 fed them with T. murina, Prof. Grassi found that in fifteen days the Tsenise 

 had mature proglottid s, and after about thirty days the eggs appeared in the 

 faeces. Closer investigation showed that within fifty hours after feeding 

 with proglottids the oncosj)heres of T. murina were found greatly increased 

 in size in the terminal ten centimetres of the small intestine, where they 

 were flask-shaped, and not unlike the bodies seen by Melnikow in Tricho- 

 dectes. The embryonic hooks are ordinarily placed on the neck of the 



* Centialbl. f, Bakteriol. u. Parasitenk., i. (1S87) pp. 305-12. 



