1. The testes of the Hermaphrodites. 23 



Meantime the cells of the region of hypertrophy (figs. 8, 9, 10, d) are proceeding on their 

 course of degeneration. These cells are derived from a germinal epithelium in all points similar 

 to that of the true germinal region. But they rapidly take on a very different character, losing 

 the conspicuous nucleolus and growing to a large size (fig. 8 Sacculina and fig. 9 Peltogaster). 

 They divide by amitosis, mitoses never being observed in this region. A further stage in their 

 degeneration is shown in figure 10 Plate 2. The greatly enlarged nuclei, crowded with chromatin, 

 are beginning to fall out of their cell bodies, leaving large honeycombed spaces in the testis 

 wall. A stage in which this process has gone further is shown for Peltogaster in figure 11, 

 where the testes wall has assumed a truly honeycombed structure owing to the degeneration 

 of the cells composing it. A section through the hypertrophied region of an old Peltogaster 

 is shown in figure 11a. 



When this process of degeneration has reached a certain stage the spermatocytes which 

 have been derived from the germinal region and have fallen into the lumen are carried to 

 the region of hypertrophy, and there lying in the honeycombed walls reach their maturity. In 

 Sacculina they must pass backwards: and when the transformations of the hypertrophied region 

 have reached a certain stage, a number of spermatocytes (sp) in various stages of development 

 can be observed lining the cavity of the testis side by side with the degenerate cells (ck fig. 12). 

 In Peltogaster the spermatocytes must pass forward to reach the region of hypertrophy, but 

 they often become mature in the germinal region itself. 



The spermatozoa are derived from the spermatocytes by the ordinary two divisions, the 

 details of which I have not worked out owing to the small size of the cells and the crowding 

 of the chromosomes. The transformation of the spermatid into the spermatozoon is shown in 

 fig. 7 a Plate 2. The spermatid is at first an oval shaped body composed almost entirely of 

 chromatic substance. It gradually elongates but retains for some time a thickening somewhere 

 along its length, often at an extremity, so that it then appears to possess a true head and 

 tail, but in reality the nucleus is drawn out into a thread along the whole length of the 

 threadlike body. In the mature spermatozoon no trace of this thickening is left and the 

 filamentous body is composed wholly of an immensely elongated nucleus surrounded by a thin 

 hardly distinguishable cytoplasmic pellicle which may be continued beyond the nucleus as a 

 true tail. The centrosome is not distinguishable for certain, though a highly refringent granule 

 can sometimes be distinguished at one extremity, and we shall see that it is equally hard to 

 distinguish, as far as my observation goes, even after the spermatozoon has entered the egg in 

 fertilization. We may compare these spermatozoa and their method of derivation with those 

 figured on Plate 8 fig. 8. In Clistosaccus (fig. 8) the young spermatids (spd) have crescent shaped 

 nuclei which gradually elongate to form the filamentous spermatozoa. In the complemental 

 males of Scalpellum vulgare I Plate 8 fig. 21) we see essentially similar changes. 



Reviewing the evolution of the testes in Sacculina and Peltogaster the most interesting 

 feature is the economy practised in the production of spermatozoa. Thus in both forms only 

 a small part of the testes produces spermatozoa, the greater part undergoing a peculiar kind 



