388 SUMMARY OF CURRENT RESEARCHES RELATING TO 



p. Nemathelmintlies. 



Hypodermis and Peripheral Nervous System of Gordiidae.*— M. 



A. Villot considers that M. Michel t has incorrectly interpreted his 

 observations. He considers that the iaypodermis of Gordius represents, 

 in the cellular stage, a layer of embryonic tissue which belongs to the 

 ectodermal layer ; the embryonic cells produce, at first by secretion, the 

 different layers of the cuticle, but this is not the only part which they 

 play in organogenesis. The cells which invest the inner wall of the 

 cloaca of adult females are converted into unicellular glands ; beneath 

 the integument they ramify and anastomose, and so form an absorbent 

 and perhaps excretory apparatus. The peripheral nervous system is 

 connected with the hypodermis by its origin and by the relations of its 

 constituent elements. It is formed of a plexus of ganglionic cells, 

 placed between the subcutaneous layer and the perimysium. The 

 ganglionic cells, which are remarkable for their small size, give off, 

 independently of their anastomoses, two kinds of prolongations. Some 

 of these are directed towards the muscular fibres, and penetrate the 

 perimysium ; others pass into cuticular papillae, which are true tactile 

 organs. 



Circum-intestinal Cavity of Gordii.ij: — M. A. Villot has a brief note 

 on the histological significance, mode of formation, and use of this 

 cavity. He regards it as the last phase in the development of these 

 round worms. It is formed by the destruction and forcing back of the 

 parenchymal cells which are found in the neighbourhood of the intestine 

 and ventral cord. These cells undergo fatty degeneration and become 

 resolved into a granular substance of yellowish colour, which lines the 

 cavity around the intestine, and fills it completely at either end. The 

 fatty matter thus produced serves as food for adult individuals living a 

 free life. After leaving their host Gordii become in a way parasitic 

 on themselves, and absorb, under the form of degenerate embryonic 

 elements, that part of their mesoderm which has not been utilized by 

 organogenesis. 



y. Platylielininthes. 



Asexual Reproductioii of Microstoma.§ — Dr. F. von Wagner has 

 made a close study of the phenomena of asexual reproduction in Micro- 

 stoma. The first step is usually the formation of a septum between the 

 second and last thirds of the body ; this is directed transversely to the 

 long axis of the body. At the same time a fold of the enteron becomes 

 fixed, and this gives the rudiment of the first bud. The size of the 

 animal thus exhibiting gemmation varies considerably. If we make a 

 general survey of the gemmations in an animal we see that the formula 

 of Hallez and Graff is often broken ; this is due to the fact that there 

 are temporary alterations in the mode and intensity of budding. The 

 enteron, the integument with its differentiations, the parenchyma and 

 the two lateral nerves pass directly from the mother individual to the 

 child, while the fresh formations of brain, eyes, ciliated pits, mouth, 

 pharynx, and glands are to be regarded as simple phenomena of 

 regeneration. 



* Comptes Eendus, cviii. (1889) pp. 304-6. f Ante, p. 225. 



X Comptes Kendus, cviii. (1889) pp. 685-7. 

 § Zool. Anzcig., xii. (1889) pp. 191-5. 



