ZOOLOGY AND BOTANY, MICK08C0PY, ETC. 737 



Finally, lie discusses the various theories of the ultimate nature of 

 fertilization. The essential fact is the process by which the sperm- 

 nucleus becomes modified into an inseparable portion — a nucleus— of the 

 ovum. The act is finished with the establishment of the male pro- 

 nucleus, the rest is developmental. The punctum saliens is the modifica- 

 tion of the nucleus of the sperm-cell into a nucleus of the ovum, and not 

 in a replacement of extruded portions of the germinal vesicle by the male 

 pronucleus. No fusion of pronuclei was observed. 



Structure and Position of Gordiacese.* — Dr. L. Camerano discusses 

 the structure of adult free-living species of Gordius, gives an anatomical 

 diagnosis of the genus, and debates the question of their systematic 

 position. Yillot regards them as an order of Nemathelminthes, 

 Vejdowsky places them as an independent order of " Nematomorpha,'' 

 and considers them as degenerate Annulata. The author maintains their 

 close affinity with Nematoda, connecting them with Acanthocephala, 

 Kinorhyncha, and further back with the Protoannelids. 



Structure and Development of Heterodera Schachtii-t — Dr. A. 

 Strubell has investigated the structure and development of this nematode 

 parasite of the tm-nip. He has no doubt that during its life-history 

 this creature not only passes through a metamorphosis, but through one 

 which is more complicated than that of other round-worms, and which is 

 of a very extraordinary character. The first larva, which has externally 

 the appearance of a nematode, is capable of movement, and lives freely 

 in earth, is succeeded by a second form in which the sexual characters 

 are also not marked, but which is sessile and parasitic, and of a plump 

 appearance. The female generative forms never become develojped 

 beyond this stage ; they remain all through their lives in a larval con- 

 dition. In the male, on the other hand, the second larval stage appears 

 to be followed by a period of quiescence, after which the mobile sexual 

 form appears, with a partial fresh formation of organs, and a further 

 development of the rudiments of the generative apparatus. 



Notwithstanding the observations of Leuckart, which have demon- 

 strated the unexpected variability of the nematode type, and have proved 

 the existence of heterogeny, no form has yet been described whose 

 history can be compared to that of Heterodera. The closest resemblance 

 is perhaps established by EchinorJiynchus, for in them, as in Heterodera, 

 there is a pupal stage, during which the old larval skin incloses the 

 new worm like a cyst. But Echinorhynclms has no second larval form, 

 the embryo, after a brief period of wandering, passing into the quiescent 

 stage. The only parallel to the otherwise isolated history of Heterodera 

 is to be found in some Insects, and particularly among the Coccidte, 

 which also lead a phytophagous life. In them there are two larval 

 stages with similar biological characteristics ; the first larval form is 

 freely mobile and of an elongated form, while the second is incapable of 

 movement and is plumper. In the Coccidse the females likewise retain 

 their larval characters, remaining sessile at one spot, and formino- a 

 brood-capsule which protects the young. The male has a somewhat 

 similar history to the male of Heterodera, for, after a pupal stage, in 

 which no nourishment is taken, an agile creature is produced, provided 

 with all the attributes necessary to copulation. 



* Arch. Ital. Biol., i^. (1888) pp. 243-8. 



t Leuckart and Chun's Bibliotheca Zoologica, ii. (1888) 52 pp., 2 pJs. 



