hargitt: pennaria tiarella and tubularia crocea. 197 



growth period the chromatin was present in the form of granules (as 

 in Tubularia) diffused through the nucleus, and a spireme or definitive 

 chromosomes were always lacking, it seems clear that the reduction 

 must have occurred during early growth, or before; the conditions in 

 Tubularia suggest that this happened in the oocyte just previous to the 

 growth. The reduction process was consequently not fully worked 

 out in either Pennaria or Tubularia alone, but in view of the close 

 relationship of these genera and their similarity in many points during 

 oogenesis and development, it seems not entirely without justification 

 to consider the process determined in part from each as giving an 

 approximately correct picture of the whole matter in both genera. 



Tetrads in the reduced number have been found in the first matura- 

 tion spindle of Tiara (Boveri, '90), Clava (Harm, :02) and Cunina 

 (Stschelkanowzew, ;06). In Linerges Conklin (:08) finds tetrads, 

 but says nothing concerning reduction, while in Gonothyraea Wulfert 

 (:02) found a reduced number of chromosomes not in tetrads. These 

 forms, then, as well as Tubularia crocea and Pennaria tiarella, give 

 evidence of a reduction occurring before the maturation spindle forms, 

 and since the germinative vesicle contains diffuse granular chromatin 

 during the growth of the egg, the reduction presumably takes place 

 before growth begins. The Hydromedusae thus seem to agree with 

 other Metazoa in the time of reduction, but the manner of reduction 

 remains undetermined. 



3. Polar-cell Formation. — In a number of Hydromedusae, includ- 

 ing Pennaria and Tubularia, the germinative vesicle has been thought 

 to fragment and entirely disappear about the time polar cells should 

 be formed. Allen (:00, p. 303) says regarding Tubularia (Parypha) 

 crocea: "I. . . .am forced to the conclusion that the nucleus of the 

 mature egg is formed by the reorganization of the fragments of the 

 nuclear matter scattered through the cytoplasm." Hargitt (:04''^, 

 :04'', :06) thinks that there may be sometimes in Pennaria, Tubularia 

 mesembryanthemum and other forms an apparent dispersal of the 

 chromatic matter of the germinative vesicle throughout the cytoplasm, 

 and IMiiller (:08) maintains for INIargelopsis and other species that the 

 disappearance of the germinative vesicle is "absolutely complete." 

 As this author finds both chromatin bodies and maturation spindles, 

 he apparently does not refer to an actual dispersal of the chromatin. 



In every egg of Pennaria and Tubularia which I have examined, I 

 have found the nucleus in some phase of its cycle. It is often very faint, 

 and is usually not accompanied by any marked concentration or 

 specialization of the cytoplasm; but no sign of its fragmentation has 



