396 SUMMARY OF CURRENT RESEARCHES RELATING TO 



essential service in the gliding movements executed by tlie parasite under 

 the scales of its liost. The stage described is that of an egg-producing 

 female ; males and females in tbe copulatory stage are scarcely one-tbird 

 the lengtb of tbe pregnant female, and nearly approach the type of the 

 free-swimming Copcpoda ; the larger males are almost normally segmented, 

 and have two pairs of swimming feet, modified to act as clinging organs ; 

 the smaller and more feebly constructed female has the segmentation 

 reduced in tbe thorax and abdomen. The testes are remarkable for being 

 moved down into the terminal segment, a change which obtains in the 

 Argulidfe, but not among Copepods ; the spermatophores are remarkably 

 large, and extend as far forward as the antepenultimate thoracic segment. 

 The prehensile antennsB are of the type of the Corycfeidae, and the two 

 winglike plates on the back of the second thoracic segment remind one of 

 the PandaridsB ; these are somewhat aborted in the ovigerous female, 

 remaining as two pointed chitinous pieces. 



Vermes, 

 o. Annelida. 



Muscular Fibres of Polychaeta.* — M. Jourdain has examined the 

 minute structure of the muscles, especially tbose of the integument, of 

 various species of Polychsetous Annelids. Though the muscular fibres 

 vary considerably in form they may be referred to two types : some are 

 almost cylindrical, others distinctly lamellar ; these are connected by 

 intermediate types. The fibres consist of a contractile substance remark- 

 able for its intense coloration and its homogeneous aspect, and of a 

 nucleus which is accompanied by a more or less abundant protoplasmic 

 body. In this contractile substance it is generally impossible to discover 

 either transverse or longitudinal strias ; staining reagents, and especially 

 hajmatoxylin, reveal segments which are alternately clear and dark, and 

 which give the fibre an appearance " plutot zebree que striee ; " these false 

 striations correspond to true thickenings of tbe muscular substance, and 

 have notbing in common with the strife of vertebrate or arthropod muscle. 

 A true striation has, however, been detected in Protula intestinum, which 

 for fineness and regularity is comparable to what is seen in mammals ; it 

 can only be detected with the aid of immersion lenses. It is to be noted 

 that tubicolous worms of the type of Protula are remarkable for the 

 rapidity with which they contract and inclose themselves in their tubes. 



Life-history of Thalassema.f — The development of a new species, 

 Thalassema mellita, has been traced from the ovum to the adult by Mr. H. 

 W. Conn. 



The ova are very minute and remain free in the coelomic fluid for a con- 

 siderable time before entering the two pairs of anterior nepbridia, or 

 " sexual pouches." As the animal when very young enters and remains in 

 the shell of Mellita, no copulation takes place. Tbe vitelline membrane is 

 excreted from the egg, which is, when discharged, filled with yolk-granules, 

 and within this membrane is a peculiar modification of tbe superficial 

 protoplasm, having the appearance of closely set, short cilia. 



The eggs are not spherical, having one pole much less convex than 

 the other, but immediately ui)on the entrance of a spermatozoon the egg 

 becomes spherical. The vitelline membrane becomes raised up over this 

 flattened area, and the polar bodies are here found — not until after the 



* Comptes Eendus, civ. (1887) pp. 705-7. 



t Stud. Biol. Ltib. Johus-Hopldus Univ., iii. (18SG) pp. 351-99 (4 pis.). See also 

 this Journal, 1884, p. 381. 



