120 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The oral and atrial muscles of Thalia longicauda have not been 

 studied, nor have the neural glands and the outgrowths from the 

 ganglion. The eye of the aggregated form has not been observed. 

 Dober (1912) gives a figure of the eye of the solitary form showing 

 little detail, but apparently indicating that the pigment is in three 

 divisions corresponding to the enlargements of the eye in the ordi- 

 nary Thalia democratica. 



The Thalias are a sharply demarcated subgenus. They grade 

 into the other subgenera less even than do the Cyclosalpas. This is 

 shown especially in the character of the eyes and the absence of neural 



0.71. u.z 



UJ 



Fio. 113. -Thalia longicauda, solitary form: A, raw from the side; B, ventral view. From 



Traustedt (1885). 



glands and outgrowths from the ganglion in the aggregated zooids, 

 but the subgenus is recognizably distinct also in the character of its 

 appendages and of the tubular protuberances from the mantle into 

 the test. In the latter two features it shows some general resemblance 

 to Traustediia. 



We have one bit of evidence that aids us in determining which of 

 the two species of Thalia is the more archaic. In studying the 

 development of the buds upon the stolon of Thalia democratica, one 

 sees that the body muscle bands arise as regularly spaced loops and 

 that only late in the development do they become approximated 



