198 ISAO IIJIMA. 



or larvse of mosquitoes, Nephelis will lay eggs in abundance. 

 Leaves of Nuphar Japonicum were kept in the vessels, and 

 on these the cocoons were always placed. In order to save 

 fresh-laid cocoons from being eaten up, it was necessary to 

 isolate the cocoon-laying individual, by removing it together 

 with the leaf to a separate vessel. This method was found 

 more convenient than keeping each in a different vessel. 



As to the time of deposit, I obtained the first cocoon of 

 this year on the 12th of April ; and last year I found freshly 

 laid cocoons as late as September 29th. 



According to A. Schneider (No. 10, p. 256), Nephelis 

 reaches sexual maturity in the spring of its second year, 

 and dies in the autumn. I have made no decisive observa- 

 tions on this point, but what I have seen has led me to think 

 that Nephelis is not a biennial animal. 



Within the cocoon is contained a fluid (Eiweiss of German 

 authors), which in a few hours after deposit hardens to a 

 transparent jelly-like consistency. If the contents of a 

 freshly-laid cocoon be examined, there will be found floating 

 in it, besides eggs, a considerable quantity of spermatozoa, 

 in a more or less broken condition, and also some pale look- 

 ing corpuscles, varying in size from a mere granule to a body 

 of "017 mm. in diameter. These bodies disappear when 

 the fluid is exposed directly to water or acetic acid. Caustic 

 potash dissolves them, and therefore, as was pointed out by 

 Rathke (No. 12), they cannot be oil globules. From the 

 fact that later they increase both in bulk and number, it is 

 evident that they are formations of the fluid itself. 



Rathke mentions the presence of short, ill-defined fibres 

 which run in uo definite direction. I have found nothing 

 of this nature, and as he makes no mention of spermatozoa 

 being present, I think he may have mistaken the fragments 

 of spermatozoa for fibres. 



Sometimes free cells, that were found floating in the 

 voarian fluid, will also be seen in the fluid. 



All the bodies above mentioned persist up to the time 

 when embryos are considerably developed, but probably 

 dissolve finally. 



III. The Structure of the Ovary-wall. 



In order to learn where and how the egg-strings arise, I 

 have found it necessary to make a careful study of the 

 minute structure of the ovary-wall, and this study has, be- 

 sides determining the point in question, brought out interest- 

 ing histological peculiarities. 



