342 7 he hish Naturalist. 



At the equator these double chromosouies arrange themselves in such 

 a manner that the plane of division between their two rod-like parts is 

 vertical and not in the equatorial plane. Seen from the poles at this 

 stage they appear triangular, quadrate or ring-shaped. Their two parts 

 are in close contact and seem fused together at their inner extremity, 

 while the outer or peripheral ends are often slightl}' parted. At the 

 equator each chromosome undergoes a horizontal longitudinal fission 

 beginning from the inner end, so that, seen from the equatorial plane, 

 the chromosome (which was at first of the typically humped form) now 

 appears X-shaped, and the two daughter-chromosomes are formed. As 

 these latter are separating from one another the rod-like arms, which 

 form them, diverge from one another so that a diamond-shaped space is 

 enclosed between the two daughter-chromosomes. As the V-shaped 

 daughter-chromosomes approach the poles, the rod-like arms of the V 

 part asunder from one another and so form twice as many short straight 

 chromosomes as there w-ere in the nuclear plate. From the process 

 described it appears probable that each chromosome in this division 

 represents two of previous divisions which have become more or less 

 completely united end to end. Their double nature is revealed in the 

 mode of origin of the two parallel portions of the chromosomes which 

 exist prior to the formation of the nuclear plate and in the separation of 

 the two parts of the daughter-chromosomes as they approach the poles. 

 From this it would appear that the reduction in number is effected by 

 an end to end fusion of the chromosomes in pairs as Strasburger has 

 already suggested as probable. 



The next division to form the pollen-tetrads takes place according to 

 the typical karyokinesis in plant-cells. 



Mr. M'ArdJvK exhibited a specimen of Fndlania dilalafa, L., which he 

 collected last year near the Baily Lighthouse, Ilowtli, which demonstrated 

 in a marked degree the facility these plants have of reproducing them- 

 selves by vegetative budding, or adventitious branching. The specimens 

 under the microscope showed all stages of development of the young 

 plantlets, which were more numerous from the leaf margins, some of 

 which bore six or more fully developed leaves, a strong shoot from one 

 of the bracteolae showed root hairs. The investigation of this 

 adventitious reproduction in liverworts will account for the continuance 

 in Ireland of plants which have never been known to bear fruit. Mr. 

 M'Ardle quoted as a familiar instance /iw^trmanm cuneifolia. Hook, known 

 to grow in the counties of Cork and Kerry for more than half a century 

 and has not been found in fruit, and may probably reproduce itself in 

 this way. 



Mr. G. H. CarMvNTER showed the springtail Lipum Wright'd from 

 Mitchelstown Cave described in the current volume of the Irish 

 Naturalist (p. 31). 



Dr. M'Weeney showed parts of the omentum of a rabbit infested 

 with the cysticerci of Tcenia serrata, Goeze. The special points of interest 

 were the presence of an outer cyst, derived from the peritoneum of the 

 host, and the small, tough, nodular cicatrix at the caudal end of the 

 vesicle. This cicatrix indicates the points of division where the worm- 

 like cysticercus, twenty-two days old, and i cm. long, splits into two equal 

 parts, of which the anterior becomes the true cysticercus, whilst the 

 posterior appears to become atrophrid and absorbed. This process takes 

 place in the liver of the rabbit before the parasite migrates into the 

 peritoneum. When the rabbits entrails are eaten by a dog, the 

 cysticercus develops into the tape-worm, which is i metre long and lives 

 in the dog's intestine. 



Mr. A. Francis Dixon exhibited two specimens of early human 

 embryos and microscopical photographs of them taken from different 

 aspects. In the youngest specimen the longest diameter of the 

 chorionic sac Mas a litlle less than 10 mm. The other specimen was 

 estimated to be in fourth week of developmeut. 



