EMBRYOLOGY OF TEREBRATULIXA. 259 



structure, and within is seen four cirri, below which the digestive cavity occurs. The tubules 

 first formed are three in number, of large size, and are arranged in a triangular figure, the 

 two forming the base of the triangle occurring midway between the front and hinder por- 

 tions of the head, the other tubule being near the anterior margin. 



The tubules, or pores first formed, present some new and interesting features. In every 

 case examined, the first that make their appearance are three in number, and are invariably 

 arranged so as to form a triangle as shown in Figures 95, 96 and 105. They are also much 

 larger than those subsequently formed. They are oval in shape, and within their borders a 

 circular, granulated plug of a reddish yellow color is seen, between which and the outer 

 border of the tubule a clear space is visible. From twelve to fourteen hairs of various 

 lengths, some of them three times as long as the diameter of the pore, spring from the 

 margin of the granulated disk, and radiate in every direction. That these are veritable 

 hairs and not minute tubules in the shell, or any internal markings, I proved in a very sim- 

 ple manner. First I made an exceedingly careful drawing of the tubule, showing exactly 

 the position of each hair, and then brushing the pores slightly with a delicate camel's hair 

 pencil I again made a careful drawing of the same pores, using the same objective, | Wales. 

 The hairs were found in every case to have changed positions, being bent in different direc- 

 tions. Fig. 100, a, represents a drawing of the tubule before brushing, though in this the 

 hairs were bent in handling the specimen, and Fig. 100, &, represents the same pore after 

 brushing. Next summer I hope to study this peculiar structure of the tubule with higher 

 powers. The tubules subsequently formed are much smaller in size, showing, however, the 

 same hairs in less number radiating from them. 



Whether there is any relation between these veritable hairs and the radiating lines sur- 

 rounding the tubules, as described by Queckett and Carpenter, and regarded by them at one 

 time as representing cilia, I cannot ay. In this connection, however, it is interesting to 

 recall other views on the subject. 1 It is more probable that the tubules are simply organs 

 of general sensibih'ty. In the test of Crustacea similar tubules occur, which penetrate to 

 the vascular layer beneath, and are regarded as endowing the test with a general sensi- 

 bility. 2 The subsequent tubules appear to make their appearance in a certain symmetrical 

 order as shown in Fig. 105, one occurring on each side of the peduncle. In Fig. 102 a dis- 

 tinct area is seen, from the anterior surface of which the cirri spring, and from the borders 

 of which the scaled structure of the calcareous shell commences to form This area has the 

 same outline as the stage represented in Fig. 94. The cirri present coarse cilia as long as 

 the diameter of the cirrus ; the cavity within is large, on the outer border of which a few 

 irregular granules are arranged in a single line. See Fig. 101, representing a cirrus from 

 stage 102. 



This brings the development of Terebratulina up to its " Early Stages," already de- 

 scribed by me in these Memoirs. 3 



By comparing the early conditions of the embryo Terebratulina with that of Thecidium, 

 described by Lacaze-Duthiers, a certain resemblance is observed, so far as the division of 



1 See an interesting paper of Prof. King on the structure Hairs of Crustacea, Philosophical Transactions, Vol. CXLVIII, 



of the tubules in the test of Brachiopoda, in the Memoirs of p. 805. 

 the Royal Irish Academy, Vol. xxiv, p. 439. 8 Morse. Early Stages of Terebratulina. Mem. B. S. 



3 See De Morgan on the Structure and Functions of the N. II., Vol. n., p 29. 



