DETELOPMENT OF THE OT ARIES IN THE BLOWFLY. 439 



paralleled plienomenou. I am by no means sure that it is so. 

 The changes in the germarium of the Trematodes described by 

 Van Beueden (5) appear to me to indicate a similar condition. 

 The nature of the germ-ova in these has been discussed with 

 great heat, some holding that the germ is a naked nucleus, and 

 others that it retains a thin, scarcely demonstrable, layer of 

 protoplasm around it. 



6. Until the actual passage of such a germ into the yelk has 

 been repeatedly observed, I admit that a serious hiatus exists in my 

 hypothesis. I am far from sure that the phenomenon has not 

 been already observed ; at any rate a passage in Leydig's mono- 

 graph (17) on the ovaries and seminal pouches of insects is 

 worthy of note in this relation. Speaking of the chorion of 

 Musca domestica, he says, " this has at the upper pole of the egg 

 a prominent micropyle which appears blocked by a highly refrac- 

 tive corpuscle. The corpuscle is not present in all the eggs, and 

 may be perhaps an exuding yelk-drop I would ask, may it 

 not equally have been an entering germ-yelk ? 



6. Bibliography/. 

 As the bibliography of the subject is given in extenso by Dr. E. 

 Stuhlmann, 1886 (25), and Dr. A. Brandt, 1878 (6), I shall give 

 only a list of the works quoted or directly made use of in this 

 paper. 



(1) Balfour, F. M.—Comparative Embryology. 1881. 



(2) Barrois. — " L'Embryologie des Nemertes." Ann. Sci. Nat. ser. 6, 



torn. vi. 1877. 



(3) Beneden, E. van. — " Recherches sur rEmbryogenie des Crustaces." 



Bull, de I'Acad. R. de Belgique, 2^ ser. torn, xxviii. 1869. 



(4) Beneden, E. v. — Ibid. torn. xxix. 1870. 



(5) Beneden, E. v. — " Recherches sur la composition et la signification 



de rCEuf." Mem. couronne's et Mem. etrang. Acad, de Belgique, 

 t. xxxiv. 1870. 



^ "Dieselbe hat am oberen Eipol eine vorsteheiide Mikropyle unci wie 

 verstopft durch ein fettglanzendes Zapfchen (Taf. iii. fig. 13Z», lAb). Dieses 

 Korperchen ist nicht bei alien Eiern vorhanden und entspricht vielleicht einem 

 herausgetretenen Dottertropfchen " {I. c. p. 35), 



