ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 753 



as complete on Carchesium polypinum, V. nehuUfera, and V. cucullus, and 

 to observe some isolated facts in V. putrina and V. microstoma. In 

 V. monilata and others the microgametes are produced by equal and 

 simple binary divisions ; in V. microstoma the binary divisions are 

 unequal and gemmaeform, while in C. polypinum they are equal, but are 

 repeated twice or perhaps thrice. 



The microgamete is only provided with a single micronucleus ; it 

 attaches itself to the macrogamete by fixing itself at first to the stalk, 

 immediately below its point of attachment to the body ; it thence ascends 

 to the lower part of the body of the macrogamete, and fuses with it. As 

 soon as it is thus fixed its micronucleus divides by karyomitosis ; while 

 this division is being effected, the two gametes coalesce. 



The micronuclei, of which one is simple in the macrogamete and 

 double in the microgamete, now grow, and four micronuclear corpuscles 

 are produced in the former and eight in the latter. Till this is done 

 the macrogamete, which has kept its peristome open, has continued to 

 feed ; it now contracts itself and closes its peristome hermetically. 

 Water accumulates within and forms a large vacuole, which pushes all 

 the contents of the body of the macrogamete backwards towards the 

 microgamete. The micronuclear corpuscles of the former have till now 

 been at some distance from the microgamete. Three of the micronuclear 

 corpuscles of the latter and seven of the former now become absorbed 

 and disappear; the two that survive increase considerably in size and 

 enter into contact. They have the form of two large longitudinally 

 striated spindles, and as they elongate they divide ; of the four micro- 

 nuclear corjDUScles thus formed two are placed in the microgamete, and 

 two in the macrogamete ; the two former become absorbed, while the 

 others fuse and form a single nucleus of mixed origin. 



Fecundation is now accomplished ; the large watery vacuole dis- 

 appears, and the contents of the microgamete empty themselves slowly 

 into the body of the macrogamete. The cilia of the peristome which 

 disappeared become renewed, the peristome reopens, and the Vorticella 

 begins to eat again. 



The new mixed nucleus now passes through several stages of division, 

 and gives rise to eight corpuscles. One of these takes on the type of the 

 micronucleus, while the other seven grow considerably. When this 

 growth has reached its maximum, and if the Vorticellae are well fed, the 

 micronucleus divides into two, and the creature undergoes fi.ssion, one 

 half having three nuclear bodies, and the other one. After two analogous 

 divisions each piece has only one large nuclear body of discoidal form, 

 which soon takes on the normal band-shape. 



The primitive nucleus of the two gametes divides into a number of 

 small spherical corpuscles, each of which persists for a long time, and 

 only disappears during the fissiparous divisions. 



It is obvious that this mode of reproduction in the Vorticellidse does 

 not differ essentially from that of other Ciliata. Notwithstanding the 

 difference in size and fate the two gametes play an identical sexual part ; 

 both possess a hermaphrodite nucleus which has exactly equivaleut 

 reproductive properties. 



Structure of Urceolarise.* — M. Fabre-Domergue has studied the 

 structure of Urceolarife both in marine and in fresh-water forms, and 



* Journ. Anat. et Physiol., xxiii. (1888) pp. 214-60 (2 pis.). 



