248 CTENOPHOR.E. Part II. 



luent ; l)ut, during the latter part of the summer of 18-58, I had ample opportunities 

 of tracing it through all its stages, and am now engaged upon a comparative study 

 of its embryology with that of Bolina and Idyia, which have appeared in unusual 

 abundance this summer. I will therefoi-e j^'^stpone the publication of my earlier 

 observations imtil the more recent ones are completed, and, in order not longer to 

 delay the printing of this volume, pass them over here, and simply state, that 

 before the young has reached one twenty-fifth of an hicli in diameter, it has 

 already assumed the appearance of the adult, while in its earlier stages it presents 

 the greatest uniformity in the three types which came under my observation. The 

 sexual organs have the same typical structure as in the other Ctenophora^, but they 

 are only distinctly visible when the spawning season approaches, late in the summer. 



Having recently seen myriads of these animals, it may not be superfluous to 

 add, that all the various attitudes in which I have formerly seen them in confine- 

 ment may be observed at one glance, when coming suddenly upon a bank of 

 them slowly drifting Avith the tide. Under these circumstances, however, they 

 are not altogether at the mercy of the current ; and it is curious to see how 

 they resist its action by stretching their tentacles in a straight line in opposite 

 directions and at right angles with the vertical axis of the body. I have also 

 satisfied myself that they are aware of the approach of danger; for day after 

 day I have seen thousands of them, which were quietly moving near the sur- 

 face with the mouth wide open in search of food, suddenly turn uj^on them- 

 selves and with a quick jerk dive into the deep as my boat drew nearer and 

 nearer. In foct, all Acalephs dive away from the surface when approached, and 

 make accelerated motions to escape the net or glass dipped into the water to 

 catch them. It seems as if they were endowed with the power of seeing, for 

 noise has no efiect upon them. 



In conclusion, I would mention the most prominent sj^ecific characters of our 

 Pleurobrachia. It is the smallest of the genus ; of remarkable transparency and 

 throughout hyaline, Avith a flesh-colored lining of the coeliac cavity, turning to brown 

 at its abactinal end and shining through the body ; the tentacles are through- 

 out rose colored, the main thread as Avell as the lateral threads ; the rows of loco- 

 motive flappers rather milk-white and iridescent. Inhabits the coasts of New Eng- 

 land and Canada, where it is seen through the whole summer. Spawns in August 

 and September. 



