76 bulletin: museum of comparative zoology. 



( Diphyopsis hispaniana.i no v. sp. 

 ( Erssea hispaniana, nov. sp. 



Figs. 98-99, Plate 39. 



Polygastric generation ~ Diphyopsis hispaniana. 

 Monogastric, sexual generation =: Ersaja liispaniana. 



Specific Characters. — Diphyopsis hispaniana. Figures 98, 99. The animal 

 is 12 mm. in lengtli. The cavity of the anterior swimming-bell is very volumi- 

 nous, so that the bell walls are remarkably thin. They are, however, quite 

 rigid, so that swimming is accomplished almost entirely by the movements of 

 the powerful velum. There is a well-developed hydroecium upon the ventral 

 side of the anterior swimming-bell, and a long spindle-shaped phyllocyst arises 

 from its inner apex, and extends upwards along the side of the bell cavity. 

 The siphosome arises from the inner apex of the hydrcecium, immediately under 

 the point of origin of the phyllocyst. The first appendage of the siphosome is 

 the large posterior swimming-bell that is almost as large as the anterior. It is 

 provided with 4 radial canals, and a circular vessel, and these are placed in 

 connection with the gastro-vascular space of the siphosome by means of a long 

 slender duct. The posterior swimming-bell possesses a well-developed velum, 

 the contractions of which acting simultaneously with those of the velum of tlie 

 anterior swimming-bell, cause the animal to dart through the water at a very 

 rapid rate. The posterior swimming-bell is provided with two large lateral 

 wings having serrated edges. The siphosome extends downward through the 

 groove between these wings. The order of development of the various organs 

 upon the siphosome is as follows : — First the feeding-polypites, then the ten- 

 tacles, then the gonads and swimming-bells, and lastly the covering scales. 

 The feeding-polypites are spindle-shaped, and quite contractile. The outer 

 surface of their proximal portions displays a number of wart-like swellings. 

 The entodermal cells of these swellings are of a decided ochre-yellow color, and 

 it seems not improbable that their function may be similar to that of the "liver 

 cells " of the feeding-polypites of Agalma. The tentacles arise from the sides 

 of the feeding-polypites very near their point of origin from the siphosome. 

 They give rise to a number of lateral branches that are studded with sharjily 

 projecting nematocyst cells. (See Figure 99.) These lateral branches term- 

 inate in swollen nematocyst batteries. The covering scales are spathiforni 

 and possess a deep ventral groove. A single gonad and a swimming-bell bud 

 out side by side, very close together, from the base of each feeding-polypite. 



When sufficiently developed, each unit, consisting in a feeding-polypite, 

 tentacle, gonophore, swimming-bell and covering scale, is set free from the 

 siphosome of Diphyopsis hispaniana, and becomes the free-swimming, mono- 

 gastric, sexual generation known as Ersaea hispaniana. 



1 Called " hispaniana " on account of its red and yellow coloration. The ento- 

 derm of the feeding-polypites being ochre-yellow, and the tentacular nematocyst- 

 batteries port-wine-red. 



