960 SUMMARY OF CURRENT RESEARCHES RELATING TO 



walls will swell and soften, and allow the eggs to escape. The importance 

 of the knowledge of the life-history of this parasite will be obvious. 



Anatomy of EcMnorhynchi.*— The Acanthocephali have been regarded 

 as devoid of a digestive apparatus, and Lespe's discovery of what he • con- 

 sidered the elementary tract in the pyriform body in the proboscis of 

 EchinorhyncMs claviceps met with but little acceptance. Eecently 

 M. P. Megnin has been studying the subject, and gave the result of his 

 researches before the Scientific Congress of Paris. 



In order to settle the question, it was necessary to study these worms at 

 a period before the development of the sexual organs, and when the nutritive 

 system was in full function. Megnin found EchinorliyncTii encysted in the 

 cellular tissue of Varanidse from the Sahara. These proved to be in a larval 

 stage, and to have a digestive apparatus composed of two long convoluted 

 tubes, each giving rise to numerous csecal diverticula. The whole presents 

 an analogy to the alimentary tract of the Trematodes. In some species, as 

 the E. hrevicoUis found in Balsenoptera sibbaldi, the digestive apparatus 

 persists and acquires considerable development. In others it undergoes a 

 degeneration, and is to be sought in the " lemnisci," structures, heretofore, 

 of problematical nature, occasionally regarded as salivary glands. The 

 larv^ have a rudimentary dorsal vessel, and this, with their proboscis and 

 aquiferous apparatus (which, however, is well developed in the adult), shows 

 the relation of the Acanthocephali to the Nemerteans or Ehynchocoela, while 

 the digestive apparatus is more like that of the Trematodes. They can no 

 longer be arranged with the Nematodes. 



Development of EcMnorhynclius gigas-j — Herr J. Kaiser has a pre- 

 liminary report on the development of EcMnorhjncus gigas. He finds that 

 the ovaries, as soon as they are set free from the ligament, appear as 

 elongate oval plasmatic discs, in which there are a number of granules of 

 various sizes, and a considerable quantity of fat-like nuclei. The latter, 

 with growth, either pass to the periphery of the ovary, increase in size at 

 the cost of the rest, and form a simple layer of polyhedral cells, which 

 invest the ovarial disc completely, or serve as nutrient material. As the 

 cells of the epithelial investment grow, their colourless protoplasm becomes 

 granular and turbid, and forms spherical structures, which move about 

 freely in the cell-capsule. The spherical gives way to a spindle-shaped 

 body, which bursts away from the ovary, and comes into contact with the 

 spermatozoa. When impregnation is effected the egg becomes surrounded 

 by a delicate clear membrane ; the nucleus disappears, and the yolk begins 

 to divide ; segmentation is very irregular. 



When there are about a dozen blastomeres a second embryonic envelope 

 appears beneath the first ; on the inner surface of the outer membrane a 

 number of dark lenticular bodies become developed, and give rise to a 

 shell, with which, in course of time, two other supporting membranes 

 become connected. 



During the development of these coverings the embryo has made further 

 progress ; there is an epibolic gastrula, and at one end the epiblast forms 

 a considerable projection, in the centre of which there are six to eight 

 nuclei ; this syncytium is clearly the commencement of the nerve-centre. 

 Later on a similar but less well developed cone appears at the aboral pole 

 of the body. The embryo now obtains its covering of spines ; between 

 every four approximating epiblast cells there arises, as a secretion-product, 

 a small thorn-like process. 



Amer. Natural., xxi. (1887) pp. 187-8. f Zool. Anzeig., x. (1887) pp. 414-9. 



