STUDIES ON THE BIOLOGY OF PARA- 

 COPIDOSOMOPSIS. 



IV. THE ASEXUAL LARV/E. 1 



J. T. PATTERSON. 



I. INTRODUCTION. 



In 1906 Silvestri 2 reported in his paper on the development of 

 Litomastix truncatellus the discovery of a curious type of larva, 

 which he regards as asexual. According to Silvestri, the egg of 

 Litomastix produces a thousand or more sexual larvse and a 

 variable number of these so-called asexual larvae. The sexual 

 larva undergoes metamorphosis and produces the adult male or 

 female insect. The asexual larva, which dies without under- 

 going metamorphosis, is characterized by the absence of certain 

 important organs, including the reproductive system. 



Silvestri has suggested the possibility that these larvae may be 

 asexual because of the absence of germ cells. In studying the 

 eggs of two monembryonic species he found that the so-called 

 nucleolus is distributed to the germ cells alone, thus serving as a 

 "keimbahm-determinant." The nucleolus is also present in the 

 egg of Litomastix. In the early cleavage stages the nucleolus is 

 included in one of the first four blastomeres, where it breaks down 

 and its contents becomes evenly scattered throughout the cyto- 

 plasm. The presence of the nucleolar material retards the sub- 

 sequent divisions of this blastomere. However, Silvestri was 

 unable to follow the history of this particular cell beyond two 

 divisions, that is, four cells. He suggests that during the course 

 of the development of the polygerm, embryos which receive 

 descendants of the single blastomere possessing the nucleolar 



1 Contribution from the Zoological Laboratories of the University of Texas, 

 No. 140. 



2 Silvestri, F., 1906, " Contribuzioni alia conoscenza Biologica degli Imenotteri 

 Parassiti. I., Biologia del Litomastic truncatellus." Ann. d. Regia Scuola 

 Superiore di Agricoltura di Portici, Vol. VI., pp. 1-51. 



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