870 Developmental History of Infusorial, Animal Life. 



which, grows by gemination and fissuration, and produces from 

 a single individual several small medusas, which again in their 

 turn produce ova. Other phenomena were soon collated with 

 these, as the fissiparous generation of Annelidas, the various 

 processes exhibited by certain Spongidas and Infusoria. In 

 1845, T. Muller described the remarkable larvae of the Eclvino- 

 dermata, from whose viscera the future perfect being is thrown 

 off by a process of gemmation ; and the researches of Kuchen- 

 rueister and Van Beneden afterwards fully illustrated the 

 remarkable migrations and metamorphoses of the Helminthoid 

 worms. " In the Distoma the embryos have at first the form 

 of ciliated monads, these are metamorphosed into Gregarina- 

 form worms, and in the interior of each of the latter, numbers 

 of Gercariform, or tailed animalcules, are developed, which 

 ultimately become true Distomata.^ 



Quatrefages and Professor Groodsir, however, look upon all 

 this as simply a part of the process of growth, comparable to the 

 growth of a lost or mutilated limb in the Crustaceas. The gemma- 

 tion of the Hydra, the medusification of the Polyp, the peculiar 

 virgin-propagation of the Aphis, the segmentation of the Nais, 

 the gradual development of the Echinoderm within its Phitean 

 larva, and all similar instances, are regarded as mere pheno- 

 mena of growth, and not as illustrations of the Parthenogenesis 

 of Owen. And this view is now held by nearly all biologists. 

 We might even go a step further and point out that recent 

 investigations have established the wide spread existence of 

 polymorphism. One of the fungi has been known to possess 

 six different kinds of fructification; the JJredo exhibits four, 

 and others might be named, which were formerly looked on 

 as distinct species. 



In some of the gemmiparous animals new creatures are at 

 times multiplied to an almost incredible extent by simple 

 mechanical division. I have seen, after breaking away an 

 Actinia from the side of my aquarium, a number of small pieces 

 of the foot-stalk left adherent to the sides of the vessel ; all of 

 which fragments became in a few days perfectly-formed young 

 Actiniae. The Hydra viridis may, as we kuow, be divided 

 longitudinally, or transversely, into several parts, and each 

 part will become a perfect polyp ; or if a wound be made 

 in the body of the animal, a new one sprouts from the site 

 of the injury. 



" The gemmiparous form of generation is met with in a large 

 variety of animals. It exists in the Infusoria, Entozoa, Polypi, 

 Medusae, Annulata and Tunicata. In the Nereis a constriction 

 first appears in the tail of the animal, immediately behind 

 which the head of a new Nereis is developed, and the posterior 

 division becomes separated from the anterior, or parent, as a 



