SUMMAKY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(principally invertebrata and cryptogamia), 



MICROSCOPY, Etc.* 



ZOOLOGY. 



VERTEBRATA, 

 a. Embryology, f 



Occurrence of Parthenogenesis.} — Everett F. Phillips gives a useful 

 summary of the most important work done on this subject. The case 

 of the honey-bee is fully discussed, not because the author considers it 

 of most importance, but simply as a basis for the subsequent treatment, 

 which covers the whole field of doubtful as well as undoubted instances, 

 from Trematodes to Mammals. Some of the facts made clear in this 

 review may be briefly stated. It is evident that parthenogenesis has 

 had a separate origin in many places in the animal scale. All that is 

 necessary in the maturation of a parthenogenetic egg is that the normal 

 n amber of chromosomes shall be retained, and this may be brought 

 about by the retention of the second polar body, by fertilisation by the 

 second polar body, or perhaps by the division of the chromosomes with- 

 out the corresponding cell-division. Parthenogenesis is generally asso- 

 ciated with, and probably caused by the necessity of the appearance of 

 a great many individuals suddenly at a certain period of the year or 

 of the life -cycle. There may be a need for females, e.g. Aphis, or for 

 males, e.g. Honey-bee, or it may be that the habits of the animal make 

 the chance of the occurrence of a sexual union too small, and in con- 

 sequence the females have acquired the agamic method of reproduction. 

 Cercaria offers a good example of this. The relation of the problem 

 of the determination of sex to that of parthenogenesis is dealt with in 

 the paper. The views put forward by various writers that the sex is 

 determined before the ova leave the 'ovary appear to receive support 

 from the facts of parthenogenesis. 



* The Society are not intended to be denoted by the editorial "we," and they 

 do not hold themselves responsible for the views of the authors of the papers noted, 

 nor for any claim to novelty or otherwise made by them. The object of this part of 

 the Journal is to present a summary of the papers as actually published, and to 

 describe and illustrate Instruments, Apparatus, etc., which are either new or have 

 not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so called, 

 but also those dealing with Evolution, Development, Reproduction, and allied subjects. 



% Proc. Amer. Phil. Soc, xlii. (1904) pp. 275-345. 



