128 WILLIAM M. GOLDSMITH. 



nucleolus, I wish to refer to the fact that many observers have 

 found the sex-chromosomes either imbedded in, or associated 

 with an achromatic nucleolus, as considered in detail in Pselliodes. 

 Although the writers referred to below did not follow in detail 

 the earlier history of the achromatic material many of their 

 illustrations and descriptions suggest a uniformity. Payne ('09) 

 finds the sex chromosomes of a number of Reduviidae embedded 

 in a plasmosome-like body as shown in Pselliodes (Figs. 17-19). 

 He notes an achromatic nucleolus and a chromatic body (later 

 the differential chromosomes) in the synaptic stage of Prionidus 

 cristatus. After this stage the achromatic material forms around 

 the chromatic body, and by fusion of the two bodies, a condition 

 similar to figure 20 is assumed. Wilson ('05) figures a close 

 relationship between the plasmosome and idiochromosomes of 

 LygcBus and Brochymena. Boring ('07) notes a true nucleolus 

 associated with an odd chromosome in Aphrophora quadrangu- 

 laris; while in the blue rove beetle, Staphylinus violaceus (Stevens 

 '08), and the earwig, Anisolabis martima (Randolph '08), this 

 body is associated with a heterochromosome. Stevens ('08) 

 notes that, "in the growth stage [of Calliphora vomitoria] the 

 hetero-chromosomes are associated with a plasmosome as in 

 many species of Coleoptera." Her Fig. n is suggestive of the 

 condition found in the early history of the nucleolus of Pselliodes. 

 The direct relation which exists between the chromatin and 

 the achromatin, clearly accounts for the erroneous theories of 

 the earlier workers regarding the origin of the true and chromatin 

 nucleolus. Montgomery ('98) states that according to his ob- 

 servations the true nucleolus is never derived from the chromatin. 

 King ('08) notes that the achromatic body (in Bufo lentiginosus} 

 is either embedded in the chromatin granules or surrounded by 

 balls of chromatin attached to the surface, and further that 

 "there is nothing to indicate that the chromatin in these struc- 

 tures (karyospheres) is derived from the plasmosome or vice 

 versa." Ruzicka ('06) considers the true nucleolus as an inter- 

 mediate stage between the chromatin and the linin. My own 

 observations have led me to conclude that in Pselliodes the true 

 nucleolus is formed by the accumulation of linin about the sex- 

 chromosomes. 



