Development of Tentacles in the Genus Hydra. 253 



margin of the bud ; and what is especially remarkable is that 

 these two elevations or protuberances are placed opposite one 

 another. I have frequently observed the first appearance of 

 the tentacles in specimens quite recently iished out of the 

 ponds, as also in artificial cultures in watch-glasses, following 

 the process in one and the same individual ; and the business 

 has always been effected in the same manner. Observations 

 made in June 1878 upon a specimen of Hydra oligactis found 

 in the same locality as the preceding species proved the same 

 thing. I may therefore say with certainty : — 1, that at the 

 commencement only two tentacles appear at once ; and, 2, that 

 these two tentacles are placed opposite each other *. 



The next stage is that represented in PI. XI I. fig. 1, ill. 

 It will be observed that the first two tentacles (a and h) have 

 become considerably elongated, and are equal in length to the 

 body of the nursing-individual. JMoreover there will be ob- 

 served between the two tentacles and on one side only a very 

 small protuberance (c), which represents the first indication of 

 a third tentacle. In other specimens I have observed inter- 

 mediate stages, in which the first two tentacles {a and h) had 

 already attained a considerable length, while the third (c) had 

 not yet appeared even in the form of a tubercle (PI. XII. fig. 2). 

 This curious creature then reminds us most strikingly of a 

 form described by Dr. T. Stre thill Wright f under the name 

 of Atracfyli's bifentaculaiaj which, he believed to be a mature 

 organism. After what I have observed in Hydra I have no 

 longer any doubt that we have in this Hydroid a similar case 

 to that which is represented in fig. 2 ; that is to say, that 

 Atractylis bitentacidata is not an independent form, but only a 

 young stage of development of some other Hydroid. This is 

 likewise the case with Atractylis quadritentacidata of the same 

 author^, which is also an embryonic form, although more 

 advanced than the former. 



The stage followin.s; that with three tentacles (ill.) is the 

 one represented in PI. Xll. fig. 3. This shows a young indivi- 



* The first appearance of a tentacle does not differ in any way, except 

 in size, from a very yoimg bud still destitute of tentacles. Again, the 

 first indications of a 'medusa are equally undistinguishable from a very 

 young individual or from a very young tentacle. This is why I have 

 already (Ann. & Mag. Nat. Hist, March L^Tb, pp. 250, 251) expressed 

 the opinion that a tentacle is just as much an individual as the body of 

 the hydranth or the manubrium of a medusa, but that, in consequence of 

 the division of labour, the tentacle individual bas been specially appro- 

 priated to the procurement of food and to defence, whilst the body itself 

 is specially devoted to digestion. In short the hydranth is a colony. 



t Journ. Anat. k Phys. i. p. 334. pi. xiv. fig. o ; and also Hincks, Brit. 

 Hydr. p. 98. ' t Loc. cif. fig. R. 



