402 SUMMARY OF CUERENT RESEARCHES RELATING TO 



development may be found in the uterus ; segmentation is irregular. As 

 noticed by Goette, two large round cells lying symmetrically in the ventral 

 region and near the middle of the body appear early ; they disappear as 

 soon as the rudiments of the gonads become apparent. Histological 

 differentiation of the various organs is effected very rapidly. In the post- 

 embryonal development of Heterodera there is a metamorphosis ; the appear- 

 ance of a pupa-stage in the male is especially interesting. The first larval 

 form is an agile worm, very much like the male in organization ; this takes 

 to a parasitic mode of life — in beet-root — and the second larval form appears 

 as a flask-shaped body ; this grows and the root of the plant incloses it. Up 

 to this stage the animals are sexually indifferent, but differences soon begin 

 to be apparent ; the greatest changes are now effected in what will be the 

 males ; the length of the whole development depends on external conditions, 

 chiefly warmth and dampness ; it is generally effected in four or five weeks. 

 The history of the metamorphosis is unlike any known among Nematodes, 

 or even in Acanthocephala ; among the Arthropoda, the greatest resemblance 

 is shown by the Coccida), where too the female remains at a larval stage. 



Asconema gibbosum.* — Prof. M. Braun, in a notice on this remarkable 

 Nematode, heads his remarks with " Atractonema gihhosum " and states that 

 in the separate copies of his paper. Professor Leuckart made a MS. 

 change of the generic name, as Asconema was already in use for a fungus. 



Structure and development of Cysts of Echinorhynchus.t — M. E. 

 Koehler comes to conclusions, with regard to the cysts of EcMnorhynchus 

 angustatiis and E. proteus found in the barbel, different to those published 

 by M. Megnin five years since. The smallest cysts, which are not more 

 than some tenths of a millimetre in diameter, a2)pear as small white dots 

 on the surface of the intestine or of the peritonfeum. They have a thick 

 envelope formed of several concentric layers of a connective tissue, rich in 

 nuclei, and there is a central granular mass formed by the union of a large 

 number of small cells. This cellular mass, which is spherical in the 

 youngest cysts, becomes ovoid, and is then differentiated to give rise to a 

 proboscis of an EcMnorhynchus on which the characteristic hooks appear. 

 The hooks are formed from before backwards. At the hinder extremity 

 of the proboscis there soon appears a small bud which gradually elongates ; 

 this is hollow and contains a central cord— the genital cord. The posterior 

 region is reduced to a very delicate prolongation, which is rounded and a 

 little swollen at its extremity, but is much narrower than the proboscis of 

 which it appears to be merely an unimportant appendage. In no case was 

 the cyst found to contain an animal provided with lemnisci, and if these 

 organs do appear within the cyst they can only do so much later on. They 

 arise behind the proboscis, and have the same structure as in the adult. 

 When the largest cysts are examined but few are found to have their 

 elements intact, nearly all are hard, and can only be broken or cut with 

 difficulty. The rudiment of the EcMnorhynchus appears to have undergone 

 a special degeneration which has made it hard and friable. 



The Echinorhynchi which are found in the digestive tract of the barbel, 

 fixed against the walls of the intestine, arise without doubt from larvfe 

 which have passed their early stages in a Gammarus or an Asellus. In 

 other words, the cysts found in the peritonaeum do not give rise to the 

 parasites found in tlie intestine. The origin of the former still remains 

 unknown, and suggestions as to it are all that can yet be made. 



* Centralbl. f. Bacteriol. u. Parasiteiikuudc, i. (1887) pp. 212-3. 

 t Comptcs Reudus, civ. (1887) pp. 710-2. 



