EMBRYOLOGY OF TEREBRATULINA. 251 



Oil the inferior side nlso of the lobule, somewhat deeply seated in the tissues, appear some red dots sym- 

 metrically placed on each siile. These spots I believe to be ej'e spots ; they are sometimes four in number, and 

 sometimes only two. The presence of these spots and of the slit, lead me to consider this extremity as 

 anterior. 



Tlie second, or large, anterior lobe is swollen behind, and nearly flat beneath. Its posterior edges run ob- 

 liquely backward to form a very obtuse angle, hardly closed on the ventral side of the large posterior lobe, 

 extending towards the angle made by the posterior lobule, which seems to be hollowed out with a wide 

 depression. 



The embryos, when the peduncle is broken, swim and whirl round by means of the cilia clothing the lobes. 

 The anterior extremity moves forward always. The. embryos are very contractile, so that, often on meetincr 

 an obstacle the longitudinal diameter becomes shorter than the transverse, the two extremities contracting 

 towards each other. The cilia then stop and seem to disappear. 



It has not been jjossible to carry the observations farther. 



To sum up, then, on the inferior aspect one of the most advanced embryos shows four eye dots, as well as 

 a distribution of the yellow material in the midst of the large anterior lobe, which reminds one much of the 

 origin of the liver in the Acephala or Gasteropoda, and it is probable that the alimentary tract is hollowed out 

 in the middle of these yellow granules, so that the secretory lobules of the liver of the adult Thecidium are 

 foreshadowed in these series of little packets. 



In the early summer of 1872 I was fortunate in tracing the embryology of Terebratu- 

 lina so for as to carry the embryo to a form with three Avell marked and deeply constricted 

 segments, and saw enough at that time to convince me that the embrj'o became attached by 

 its caudal segment. These meagre results were pubhshed in Silliman's Journal.'' 



Some interesting features, however, had been brought to light in studying the early 

 stages of certain Brachiopoda, the most important of which were presented by Fritz 

 Miiller in a note pubhshed m Eeichert und Du Bois-Rej^nond's Arcliiv, 1860, p. 72, and 

 a subsequent note in Wiegiuann's Archiv, 1861, p. 53. These notes referred to the early 

 stages of a form supposed to be Discina, collected at Santa Catharina, Brazil. I suljjoin 

 the notices which were pubhshed in the Annals and Magazine of Natural History, 3d series. 

 Vol. VI., p. 310. 



'' Dr. F. Mailer has sent from Brazil the description of a larva belonging undoubtedly to a Bracliiopod, 

 which is the more interesting, as the Brachiopoda are the only Mollnsca regarding the development of which 

 we have no infoiTnation. 



" Tlie larva in question is a small, perfectly orbicular, bivalve Mollusk. The two valves are similar, but un- 

 equal in size, the dorsal valve being the largest. At the place of the hinge a small oval plate is placed trans- 

 versely between the two valves of the shell. The mantle is gaping all round. Five pairs of very stiff setie, 

 of which one is much stronger than the others, and curved backwards, project at the periphery. They ori<'>'i- 

 nate in the mantle of the ventral half; at least tliis is the case with four of them. A series of finer sette 

 S])ring from the circumference of the mantle of the dorsal valve, an<l curve down upon tlie outside of the 

 ventral valve. The animal, as well as the shell, would be divided into two symmetrical halves by a plane 

 drawn veitically through the middle of the hinge. The body, which is furnished with an alimentary canal, 

 two auditory capsules, and two eyes, fills the posterior half of the space between the valves. The anterior 

 half is oecui)ied by four pair of cylindrical arms, between which a rounded knob is situated. Behind the 

 knob the month is perceptilile. 



"These four pair of arms are supported upon a common peduncle, at the extremity of which, therefore, tlie 

 mouth is placed. The arras are covered with a very well developed ciliary coat, by the agency of which the 

 little animal swims. The reproductive and circulatory organs are wanting. 



"During natation the mouth is always directed forwards, which is in favor of the generally received opinion 



1 Am. Jour. Science and Arts, iv., 1S72, 2G2. 



