INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 79 



The early appearance of the rudiments of the generative organs 

 is not only to be observed in Moina ; Metschnikoflf bad already noted 

 it in the case of Miastor and Aphis ; and in all these three forms 

 eggs are developed parthenogenetically. What is the connection 

 between these two phenomena ? is the early develojiment of the 

 generative organs the cause of pai'thenogenesis, or has partheno- 

 genesis effected their earlier appeai-ance ? The latter would appear 

 to be the better reason, inasmuch as no such early development has 

 been observed in the parthenogenetic Lepidoptera and Hymenoptera. 

 Again, the organs in question do not exhibit their activity till all the 

 other organs are fully developed, and natural selection could not, 

 therefore, have exerted any influence in fixing the earlier date of their 

 a2)pearance. 



It is of especial interest to note that there is a directive corpuscle 

 in the developing ovum, inasmuch as it has been supposed that the 

 absence of this body might be associated with the absence of an 

 immediate fertilizing agent.* Dr. Grobben is, however, of opinion that 

 parthenogenesis is a mode of sexual reproduction, although he appears 

 to agree with Weissmann in regarding it as unisexual, and he looks ujion 

 the ejection of the corpuscle as due to the fact that the partheno- 

 genetic egg has been derived from one which was fertilized. In fine, 

 he distinguishes the mode observed in Moina from true partheno- 

 genesis by a grouping of the phenomena which may be thus 

 recapitulated : — Reproduction may take place (1) by means of the 

 germ-layers of the mother — asexual reproduction ; and this may bo 

 (a) by fission or [h) by gemmation; (2) by means of one cell aided 

 by another cell — sexual reproduction ; and this may be unisexual, i. e. 

 (a) parthenogenetic, or (b) bisexual. 



In all cases of heterogony there is a periodic appearance of the 

 male. Kurz thinks that the male appears among the Cladocera only 

 when the female finds the quantity and quality of the water it inhabits 

 insufficient, and Weissmann regards its appearance as owing to the 

 general conditions of existence. Grobben looks on the male as being 

 produced from the necessity of its occasional presence for an 

 cflcctual development by means of fertilization. 



Compound Eye and Cervical Organ of the Phyllopoda.t — In the 

 developmental history of Moina, we may see that the eye becomes 

 overgrown by a fold of the ectoderm from behind and from the 

 ventral side, and that it thus becomes covered by two membranes ; 

 one is in direct connection with the cornea, and the other forms an 

 integumentary investment ; and this arrangement is constant among 

 the Phyllopoda. It is obvious that it has for its purpose to protect 

 the eye, and we may expect that in all cases where the eye is movable 

 without being stalked, similar arrangements will be found to obtain, 

 and the author siiggcst.-i that observations should bo made on the 

 Copepoda, Ostracoda, and Arachuida with this special point in 

 view. 



The importance of the cervical organ lies in the light which it 



* Cf. Bulfuur, ' Quart. Journ. Micr. Sci.' (1S7S). 

 t 'Arbeit. Zo<j1. lust. Wurzburg,' ii. (IbTJ) loc. tit. 



