EMBRYOLOGY OF TEREBRATULIXA. 251 



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

 metrically placed on each side. These spots I believe to be eye 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. 



The 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 meeting 

 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 possible 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 far as to carry the embryo to a form with three well marked and deeply constricted 

 segments, and saw enough at that time to convince me that the embryo became attached by 

 its caudal segment. These meagre results were published in Silliman's Journal. 1 



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 published in Reichert und Du Bois-Reymond's Archiv, 1860, p. 72, and 

 a subsequent note in Wiegmann'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 subjoin 

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

 Vol. vi., p. 310. 



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

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

 we have no information. 



"The 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 setae, 

 of which one is much stronger than the others, and curved backwards, project at the periphery. They origi- 

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

 spring from the circumference of the mantle of the dorsal valve, and curve down upon the outside of the 

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

 drawn vertically 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 occupied by four pair of cylindrical arms, between which a rounded knob is situated. Behind the 

 knob the mouth is perceptible. 



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

 mouth is placed. The arms 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., 1872, 2C2, 



