2O6 GEO. W. TANNREUTHER. 



not be distinguished from the ordinary interstitial cells except 

 during the period of sexual reproduction. Fig. i, a and b, rep- 

 resents two adjacent eggs at the stage of development when they 

 first become recognizable. They have begun to enlarge and can 

 readily be distinguished from the adjoining cells by their size and 

 vacuoles next the nucleus. The above figure was taken from an 

 adult hydra in which six eggs were present in different stages of 

 development, ranging from the interstitial cells to the undisputed 

 egg. These eggs are isolated or found in groups. When two or 

 more are found adjacent the cell walls become dissolved and one 

 persists as the developing egg (Tannreuther). In a few in- 

 stances observed two of these adjacent cells persisted and gave 

 rise to two mature eggs. These cases, however, are extremely 

 rare in proportion to the number of eggs produced. 



The above results do not warrant the view that there is con- 

 tinuity of germ plasm in Hydra. Until sex cells distinct from 

 the somatic can be traced through successive generations, we have 

 no positive evidence of such a continuity. 



The different generations of the sex cells of Hydra are distinct 

 and can readily be recognized. In the formation of the egg there 

 is a distinct growth period. Reduction occurs at the end of the 

 growth period just before the first polar body is formed. The 

 polar bodies remain attached after cleavage has begun, by means 

 of a single cytoplasmic thread. The first polar body is larger 

 than the second. 



The spermaries are composed of an indefinite number of cysts. 

 The individual cysts originate from a single or several interstitial 

 cells. Fig. 2 represents a longitudinal section of a single cyst 

 containing spermatogonia, which have originated from a single 

 interstitial cell. After the spermatogonia have divided a few 

 times (the number of divisions varies in different individuals) 

 those found at the distal end of the cyst become transformed into 

 the spermatocytes of the first generation without growth. In 

 Fig. 3 the spermatocytes of the first generation are recognized by 

 their dense chromatin mass. Different stages of development are 

 found in a single cyst, ranging from the spermatocytes of the 

 first generation to mature sperm, as shown in Fig. 4. The suc- 

 cessive zones of the developing sperm are distinct. The nuclei 



