226 



THE AMERICAN MONTHLY 



[December 



between its body-cavity and that of 

 the parent is at first uninterrupted, 

 and food captured by either indi- 

 vidual seems to be appropriated by 

 both. Gradually, however, a con- 

 striction occurs at the point of con- 

 tact, and finally complete separation 

 ensues. Very frequently several 

 young Hydra; are attached to the 

 parent, and buds are in turn often 

 developed on these before they leave 

 the parent stem. Carpenter copies 

 an old figure from Trembley's work 

 in which an individual of II. fiisca 

 is shown w^ith no less than nineteen 

 young polypes attached in various 

 stages of development. Kleinenberg 

 has made the interesting observation 

 that where an individual of H. vi?-i- 

 d/s, with a nurherous progeny at- 

 tached, was placed in a glass con- 

 taining very little food-material, in 

 the course of a few weeks first the 

 bodies and then the tentacles of the 

 young animals were re-absorbed by 

 the parent Hydra. 



Of all the many marvelous proper- 

 ties possessed by this remarkable lit- 

 tle organism perhaps the most extra- 

 ordinary is its power of reproducing 

 lost parts. The researches of Trem- 

 bley and Baker on this peculiarity are 

 even at this date well worthy of peru- 

 sal. To quote from one authority : — 

 ' If the body be cut into two or more 

 — even into forty — parts, each portion 

 continues to live and develop a perfect 

 new animal. If the section be made 

 lengthwise, so as to divide the body, 

 all but the end, the two portions be- 

 come re-soldered, and form a perfect 

 being ; if the pieces be kept asunder, 

 each becomes a Hydra, the two pos- 

 sessing but one posterior end ; if the 

 section be made towards the head, 

 the two bodies will be perfected and 

 remain attached to the one head If 

 a tentacle be cut oft', a new animal is 

 formed from it. When one end of the 

 body of a Hydra is introduced into an- 

 other, the two unite and form one ; the 

 head cut oft' one may be engrafted up- 

 on the body of another which wants 

 one ; and when the body is tvn-ned in- 



side out, the outer surface, which has 

 thus become the inner, will perform 

 the ordinar}^ digestive functions, and 

 the animal will continue to live.' 



Most of these statements have been 

 verified times without number, but the 

 correctness of the last one (referring to 

 tvu'ning the Hydra inside out) seems 

 to lack confirmation, although the ex- 

 periment is described at considerable 

 length by Trembley, who was cer- 

 tainly otherwise a careful observer. 

 A Japanese naturalist. Prof. Mitsi- 

 kuri, is reported to have recently 

 succeeded in verifying Trembley's 

 experiment, but all other investiga- 

 tors appear to have completely failed 

 therein ; and it certainly seems to me 

 that, in view of the strongly-marked 

 diftbrence in character and function 

 between the endoderm and ectoderm, 

 a forcible reversal of the relative po- 

 sition of these layers would make the 

 assimilation of food absolutely impos- 

 sible, and would, therefore, inevitably 

 result in the speedy death of the polype. 



As might be expected in the case 

 of an animal whose vital powers are 

 so phenomenal, abnormal growths 

 of Hydra are of frequent occurrence. 

 Double rows of tentacles, loops in the 

 body, 'Y' shaped tentacles, &c., 

 have often been seen. 



Hydra is frequently found infested 

 by large nvuribers of small ciliated in- 

 fusoria, viz : — Trichodiiia pedicu- 

 his, Ehr. (fig. 33). They either ad- 

 here closely to the body and tentacles 

 of the polype or glide rapidly to 

 and fro over those surfaces, unaftected 

 by the stinging organs or by the con- 

 tractile movements of their host. 

 Most authorities state that their pres- 

 ence is not detrimental to Hydra, 

 but I have invariably found that when 

 the latter was thus infested it did not 

 thrive well. Another infusorian, 

 Keroiia polyporum, is frequently 

 found similaily infesting the polype. 



The geographical distribution of 

 Hydra is known to be very wide. 

 Certainly throughout the temperate 

 zones this interesting organism is 

 plentifully found in suitable localities. 



