540 . A. C. WALTON 



of the nucleus. . Marcus ('06) finds in A. canis (?) a s'milar be- 

 havior of the nuclear elements during the formation o the net- 

 work and spireme from the oogonial chromosomes, except that 

 the threads appear to be paired, or at least to lie parallel with 

 one another, most often in twos. In the oocytes of A. megalo- 

 cephala, Hertwig ('90) finds that the doubleness of the spireme 

 thread may or may not be evident at this stage, although it is 

 generally evident n the spermatocytes. Schleip ('11) contends 

 that in Angiostomum nigrovenosum the parallel threads of the 

 spireme are due to a longitudinal splitting of one thread, not to 

 a pairing of two separate threads. A. canis shows no evidence 

 of this double nature of the spireme threads, either through 

 splitting or pairing. 



The cells become very closely packed (fig. 11), assuming 

 angular outlines, and some even appear to have lost all con- 

 nection with the rhachis. This cord, beg'nning as a fine thread 

 in the anterior end of the oviduct, sends off, as it grows back- 

 ward, four primary lamellae, to which the oogonia are attached 

 n a single layer. The peripheral margins of the primary lamel- 

 lae bifurcate, and in the region of the primary oocytes 

 sexual cells are attached both to the four primary lamellae and 

 to the eight secondary ones, but always in a single layer. The 

 secondary lamellae quickly become so obscured by the crowding 

 of the rapidly growing cells (fig. 11) that they are easily over- 

 looked, and the oocytes thus appear several layers deep around 

 the primary lamellae. Careful study, however, shows that each 

 of the cells is in reality directly attached to the rhachis by a 

 fine stalk. This shortening and thickening of the primary 

 lamellae and the practical disappearance of the secondary lamel- 

 lae agree with the condition described by Hertwig ('90) for both 

 types of A. megalocephala, but Schleip ('11) finds that in An- 

 giostomum nigrovenosum the growth takes place after the break- 

 ing down of the rhachis and the setting free of the' oocytes. In 

 a Sclerostomum from the horse, Kiihtz ('13) shows that the 

 growth is completed (zone of growth) before the breaking down 

 of the rhachis. 



Following the stage illustrated in figure 10, the chromatin 



