292 SUMMARY OF CUERENT RESEARCHES RELATING TO 



Development of Rhabditis aberrans.* — Eva Kriiger finds that 

 almost all the individuals of this new species of Rhabditis are somatically 

 females, but in their gonads protandrous hermaphrodites. The sperma- 

 tozoa appear at the beginning of the sexual maturity and collect in the 

 receptaculum seminis. If ova pass into the receptaculum, the sperma- 

 tozoa enter, but their nucleus does not unite with the ovum nucleus. 

 It degenerates in the cytoplasm of the ovum, and the development of 

 the ovum is parthenogenetic. Only once did the observer see the 

 formation of a second polar body and the union of sperm-nucleus and 

 ovum-nucleus. The result is unknown. 



Besides the females there are a very few males (0*4 p.c). These 

 have a degenerate sexual instinct. On one occasion the males rose to 

 16 p.c, but they were none the less sexually degenerate. 



The spermatogenesis is described. Each spermatid has normally 

 nine chromosomes, of which one is a sex-chromosome. In some cases 

 there are two kinds of spermatozoa, only half of them having a sex- 

 chromosome. 



Species of Microfilaria.f — H. Foley has made a careful comparison 

 of the two ensheathed species common in man in Algeria — Microfilaria 

 hancrofti and Jlicrofilaria diurna. He shows how they differ in Griemsa 

 preparations. The former lias a strongly-stained sheath ; the nuclei 

 appear blue ; the nuclei at the cephalic end lie in a straight line ; the 

 somatic nuclei are smaller, more rounded, more regular, more easily 

 counted ; the nuclei of the caudal end do not reach the point ; the 

 central body stains well. In the second species, the sheath remains un- 

 stained ; the nuclei appear blue-violet ; the cephalic nuclei are more or 

 less irregular ; the somatic nuclei are larger, less regular, sometimes 

 fused, occupying the whole length of the embryo ; the caudal nuclei 

 extend to the very tip ; the central body was not visible. 



Development of Gordius aquaticus.J — N. Th. Meyer finds that 

 the formation of the inner layer of the embryo is due to a unipolar 

 immigration. This process represents an early segregation of the mesen- 

 chyme. It seems to the author that the gut is originated from two 

 invaginations which grow in opposite directions and finally fuse in one 

 tube. The posterior invagination, which appears first, represents the 

 mesenteron and also the proctodaeum. Meyer has observed that the 

 primordium of the pro])oscis is due to a second invagination at the 

 anterior end of the embryo. In the larva there are no visible primordia 

 of the gonads. 



Platyhelminthes. 



Plerocercoid from Pig'.§ — S. von Ratz describes Sparganum raillieti 

 sp. n. from pig's muscle. It has the form of a "plerocercoid." A 

 plerocercoid is that type of Cestode larva which consists of a head and a 

 parenchymatous tail portion into which the head is often retracted. The 



* Zeitschr. wiss. ZooL, cv. (1913) pp. 87-124 (4 pis.). 



t Ann. Inst. Pasteur, xxvii. (1913) pp. 50-88 (1 pi.). 



X Zeitschr. wiss. ZooL, cv. (1913) pp. 125-35 (2 pis.). 



§ Centralbl. Bakt. Parasitenk., Ixvii. (1913) pp. 523-7 (3 figs.). 



