146 Reviews. [Jan., 



that their community of habit and similar life-history, combined with 

 the great practical advantage of studying them together as parasites 

 offensive and injurious to the human body, justify their union. 



The following is Dr. Cobbold's proposed scheme of classifica- 

 tion : — 



Class 



[c, i ! T c , (Old. 1. Turbellaria 



, Sub-class . Sterelmintha j 0rd _ 2 Trematoda 



Helmintha <j Sub - clasa ILCiELELMiNTHA Orel. 3. Nematoda 1 Entozoa . 



I q i i ttt a ™ f Ord. 4. Acanthocepnala | 



j Sub-class ni. Anenteeelmintha) Qrd 5> Cestoda> * j 



This is a good practical classification, and by placing the Thorn- 

 headed worms (Acanihocephala), and Tape-worms (Gestoda), in a sepa- 

 rate sub-class, the other two sub-classes have been undoubtedly 

 strengthened. 



The propriety also of placing the Turbellarian worms — Planaria, 

 and Nemertes, with their congeners, near to the Trematode worms, will 

 at once be apparent to all those who have studied these comparatively 

 neglected organisms. 



After having settled the questions that may arise out of his general 

 classification, Dr. Cobbold proceeds to illustrate each of his orders. 

 In this part of his work he takes up some particular species, and 

 gives an account of its anatomy, development, habits, and distribu- 

 tion. In the description of the Turbellaria, reference is made to the 

 curious fact of the extensibility of the species of Nemertes. One of 

 these, N. Borlasii, is said to be capable of stretching itself to fully 

 eight times the length of the body whilst at rest, so that the animal 

 which is ordinarily four or five feet in length, is capable of assuming 

 a length of forty or fifty feet. These worms are, however, not entozoa. 



The second order, Trematoda, are true entozoa, and are com- 

 monly known by the name of flukes. This order is composed of 

 five families, which are mostly characterized by the number of open- 

 ings upon their flat bodies, which have given the family its name. 

 These creatures are found in the bodies of men, mammals, birds, and 

 fishes. Dr. Cobbold has described several species. In a recent in- 

 vestigation of the number of species described, he says, " I recog- 

 nized 344 species of flukes, 126 of these belonging to fishes, 47 to 

 reptiles, 108 to birds, 58 to mammals, and 5 to invertebrata." This 

 did not include those forms which are found attached to the skin of 

 animals, which would probably raise the number to .400 species. It 

 is in this family that Van Beneden originally observed the curious 

 phenomena of " nursing ; " but which really consists of the offspring 

 of the original parent being capable, at certain stages of their growth, 

 of producing new individuals. This offspring, the larval " great- 

 grand-children," are the previously known Cercarice, which ultimately 

 become transformed into a form similar to the first parent. Dr. 

 Cobbold gives an interesting account of his observations on Gyrod- 

 actylus elegans, one of the most highly developed of the Trematodes, 

 and which he obtained from sticklebacks, caught in the Serpentine. 



The Nematode, or thread-like worms, come next. These are 

 arranged in eight families. First among them is a group familiar 



