26 Papers from the Marine Biological Laboratory at Tortugas. 



a giant spermatid (with the accessory chromosome, of double size in this 

 case) in process of metamorphosis, and a fully formed giant spermatozoon. 



Giant spermatozoa have been frequently observed among the insects. 

 Wilcox (1895) found them extensively and made a study of them in 

 Cicada tibicen and Caloptenus femur-rubum. With Wilcox, I believe that 

 they are non-functional also in Aplopus maycri, and that " they are excluded 

 from the developmental series and really come to nought." 



I have noted above that the primary spermatogonial cell frequently 

 divides amitotically. This may occur several times, giving rise to a multi- 

 nucleate cell. Contrary to what Wilcox has found in Cicada tibicen, where 

 the giant spermatozoon " arises directly from spermatogonia without cell- 

 division, by a metamorphosis of the nucleus," figure 24 shows that the 

 binucleate cell resulting from an amitotic nuclear division may subsequently 

 divide karyokinetically. Such a cell would give rise to spermatocytes of 36 

 chromosomes (which have been observed) and eventually to giant sperm- 

 atozoa. I have not observed spermatocytes with 72 chromosomes, but such 

 may very well arise as a result of two successive amitotic nuclear divisions. 



Frequently spermatids are seen with two or even several tails. This 

 phenomenon is due probably to an accidental or abnormal division of the 

 centrosome, from each product of which an axial filament grows out. Adult 

 spermatozoa thus deformed are only seldom seen ; they probably early 

 undergo degeneration. 



THEORETICAL CONSIDERATIONS. 



INDIVIDUALITY OF CHROMOSOMES. 



Among the ordinary chromosomes morphological individuality can not 

 be convincingly demonstrated. This is due to the fact that between every 

 mitosis, both spermatogonial and spermatocytic, as well as previous and sub- 

 sequent to synapsis, a brief resting stage is interpolated when the chromo- 

 somes are merged into the nuclear reticulum. Correspondence of size can 

 readily be found between the chromosomes of the equatorial plates of the 

 primary and secondary spermatocytes, as also between these and pairs of 

 chromosomes of the spermatogonial mitoses, but I do not consider the corre- 

 spondence sufficiently close or striking to contribute reliable evidence in 

 favor of the above hypothesis ; nor do I believe it possible to find very strong 

 evidence from this source in cases where we are dealing with so large a 

 number of chromosomes. What evidence there is, however, points in the 

 proper direction, as will be noticed by comparing figures 17, 74, and 114. 



The evidence yielded by the accessory chromosome, however, is definitely 

 corroborative of this hypothesis. When once fully differentiated in the later 

 orders of the secondary spermatogonia it retains thereafter a persistently 

 definite shape, size, and location in the nucleus, and never passes into a 

 reticular stage. Even when assembled among the ordinary chromosomes of 



