LEWIS R. GARY. 



sind, indem jede aus zwei bilateral angeordrjeten, vollstandigen 

 Mesenterienpaaren besteht." Besides these three types Carl- 

 gren recognizes a mixed type which cannot be put in any one 

 of the above-mentioned classes. 



All the specimens of Aiptasia studied by Carlgren fell, with 

 three exceptions which were very irregular in their growth, into 

 his group three, the biradial type, in which there are two zones 

 of new growth. All of the specimens of this genus that I have 

 sectioned show this arrangement of the newly formed mesenteries, 

 which, thus, seems to be characteristic of the genus Aiptasla. 



The specimens of Cylista also showed the same arrangement of 

 the first mesenteries. 



H. V. Wilson, 1888, states that in Macina areolata the ceso- 

 phageal invagination is at first centrally placed in the larva, but 

 that soon "it begins to travel toward one side of the larva." 

 This lateral motion of the stomodeum continues until that organ 

 comes to lie close against the outer wall of the larva. Finally 

 as the lateral movement progresses from above downward 

 the endoderm is pushed before it until the two ectodermal layers, 

 of the stomodeum and of the body wall, are in contact, or sepa- 

 rated only by the thin layer of mesoglea secreted between them. 

 Soon following this stage,- . . . "the oesophagus has moved away 

 from the surface ectoderm, but while doing so has remained 

 connected with it by a band of supporting lamella." The mes- 

 entery arises by the endoderm growing up into the space between 

 the stomodeum and the outer wall of ectoderm as the stomodeum 

 is drawn toward the side opposite the first mesentery, for the 

 formation of the second one. 



Appellof, 1900, mentions the same sort of displacement of the 

 stomodeum previous to the formation of the first mesentery. 

 He states, on the other hand, that: "Die exzentrische Lage des 

 Schlundrohres ist in alien Entstehungsphasen desselben konstant 

 und deutlich nachzuweisen und ist so nehme ich wenigstens 

 an auf ungleichseitiges Wachstum der Larve zuriickzufuhren." 



In laceration embryos the stomodeum is from its first appear- 

 ance excentric in position. As the change in the form of the 

 piece takes place so that the original orifice, where the piece was 

 torn off from the parent, becomes carried up toward the highest 



