38 AMERICAN HYDROIDS. 



diately recognizable as a young gonaiigium (fig. 99). At first, strangely enough, the endoilerm 

 layer does not carry the spermatoblasts with it into the young gonaiigium. Afterwards the 

 sperinatoblasts migrate en masse with a flowing motion, passing through the opening in the perisarc 

 and up into the blastostyle. Weismann believes that this movement is due, in part at least, to 

 the activity of the individual sperinatoblasts, from the fact that they become scattered during the 

 operation. 



The gonaiigium itself (fig. 102) is formed primarily by the delicate inner pellicle of perisarc 

 which is pushed out by the growing ectoderm cap. Later this appears to be reeuforced by a 

 secretion from the peripheral ectodermal cells, appearing as a clear transparent fluid, which 

 evidently hardens into chitine. After attaining a definite thickness, which it does very soon, it 

 does not further increase in thickness, although the gonaiigium attains a much greater size 

 before it reaches maturity. 



The gonophore now develops rapidly, the first indication of its location being an aggrega- 

 tion of the spermatoblasts in a definite locality, where they form a protuberance in the endodenn 

 of the blastostyle. Next the spermatoblasts pass through the stutzlamelle and take their place 

 between that structure and the ectoderm (fig. 97). This appears to occur very early in the history 

 of the structure. 



The present writer found in his study of Plumularia pinnata that the spermatoblasts under- 

 went a certain amount of cell division before penetrating the stutzlamelle. 



Afterwards the gonophore is formed by a budding from the blastostyle very much as the 

 latter was formed from the C(enosarc of the stem, although in the former case there is no ectoderm 

 cap formed, as there is no perisarc to be penetrated. The gonophore, then, is a two-layered sac 

 composed of ectoderm and endoderm separated by the stutzlamelle, but with the rapidly increasing 

 mass of sperm cells between the ectoderm and stutzlamelle. The cavity of the blastostyle com- 

 municates with that of the spadix or central core of the gonophore, and in living specimens a 

 great activity is seen, rapidly moving currents being constantly swept to and from the cavity of 

 the gonophore (fig. 99). 



Weismauu says that the histogenesis of the semen cells has not been followed. My own 

 observations show that there is a further and often-repeated division of the spermatoblasts after 

 they have penetrated the stutzlamelle, the ultimate result of these divisions being spermatozoa 

 which at first have large heads and short tails, but gradually reverse these proportions until the 

 typical form is reached. As the spermaries reach maturity, the cap of elongated ectoderm cells 

 occupies the end of the gouaugium, and, extending downward, meets the endodermal layer, the 

 whole structure forming a sort of plug which fills the distal end of the gonaiigium (fig. 96, d k p). 

 This plug seems to be partly absorbed when the spermatozoa reach maturity; and when the 

 spermaries break, the plug is in some way penetrated by the spermatozoa which finally escape 

 to the outer world through an aperture in the end of the gonaugium. 



In Plumularia pinnata I found that the entire goiiophore would at times break through at the 

 top of the gonaugium, appearing much like an acrocyst such as is found in Sei-tnlnria j>in><n<i, 

 although, of course, it was very different homologically (fig. 101). It is not impossible, however, 

 that the gonophores may have been accidentally forced out of the gonangia by external pressure, 

 although care was taken in the handling of the specimens. In mature gonophores the spermatozoa 

 seem to be arranged in numerous lines radiating from the spadix (fig. 100). 



In /'. rcJiinitldta a second gonophore is formed, the only difference being that in this case the 

 "Hodeii" are formed in the blastostyle instead of in the stein. In P. pinnaia as many as a half 

 dozen gonophores may be seen on the same blastostyle (fig. 101'). In one case Weisuiann found 

 that the mass of spermatoblasts while still in the internode of the hydrocladium became 

 developed into a gonophore of thin perisarc, and thus the internode performed the role of the 

 blastostyle. 



The origin of the female sex cells is quite similar to that of the, male elements. The cells 

 originate in the endoderm of the stem and basal internodes of the hydrocladia; the "Keinizone" 

 is here, as in the male colony, immediately above the developed gonaugia. In the tipper 

 iuternodes of this zone appear ''Keimzellen," such as are found in the male, of irregular outline 

 and size. Instead of repeatedly dividing and decreasing in size, however, these, cells grow larger 

 and eventually become well-marked ova, which often exhibit amu-boid movements and contain 



