EMBRYOLOGICAL SYSTEMS. 365 



the development of Mollusks evolutio radiata, especially 

 after Baer had designated, under that same name, the 

 mode of formation of the branch of Eadiates, for which it 

 is far better adapted. 



CLASSIFICATION OF YOGT. 



Contrast between the Embryo and the Yolk, 



I. VERTEBRATA. Yolk ventral. 



CL. 1. MAMMALIA. 1. APLACENTARIA ; Orel. Monotremata, Marsu- 



pialia. 2. PL A CENT ARIA. Ser. 1. Orel. Cetacea, Pachy- 



derrnata, Solidungula, Ruiniuantia, and Edentata; Ser. 2. 



Pinnipedia, Carnivora; Ser. 3. Insectivora, Volitantia, Gli- 



res, Quadrumana, Biruana. 

 CL. 2. AVES. Ser. 1. Insessores; Ord. Coluinbe,Oscines,Clainatores, 



Scansores, Raptatores ; Ser. 2. Autophagi ; Ord. Natatores, 



Grallatores, Gallinaceae, Cursores. 

 CL. 3. REPTILIA. Ord. Ophidia, Sauria, Pterodactylia, Hydrosauria, 



and Chelonia. 



CL. 4. AMPHIBIA. Ord. Lepidota, Apoda, Caudata, Anura. 

 CL. 5. PISCES. Ord. Leptocardia, Cyclostomata, Selachia, Ganoidea, 



Teleostia. 



II. ARTICULATA. Yolk dorsal. 



CL. 6. INSECTA. Subcl. \. AMETABOLA; Ord. Aptera. Siibcl.2. He- 



mimetabola ; Ord. Hemiptera and Orthoptera. Subcl. 3. 



Holometabola ; Ord. Diptera, Lepidoptera, Strepsiptera, 



Neuroptera, Coleoptera, Hymenoptera. 

 CL. 7. MYRIAPODA. Only divided into families. 

 CL. 8. ARACHNIDA. Ser. 1. Pycnogouida and Tardigrada ; Ord. Aca- 



rina, Araneida. Ser. 2. With three families. 

 CL. 9. CRUSTACEA. Subcl.l. ENTOMOSTRACA; Ord. Cirripedia, Para- 



sita, Copepoda, Phyllopoda, Trilobita, Ostracoda. Subcl. 2. 



XIPHOSURA. Subcl. 3. PODOPHTHALMA; Ord. Stomapoda, 



Decapoda. Subcl. 4. EDRIOPHTHALIA; Ord. Leemipoda, 



Amphipoda, Isopoda. 



Transformation of the ivhole Yolk into the Embryo. 



III. CEPHALOPODA. Yolk cephalic. 



CL. 10. CEPHALOPODA. Ord. Tetrabranchiata and Dibranchiata. 



IV. MOLLUSCA. Irregular disposition of organs. 



CL. 11. CEPHALOPHORA. Subcl. 1. PTEROPODA. Subcl. 2. HETERO- 

 PODA. Subcl. 3. GASTEROPODA ; Ord. Branchiata and Pul- 

 monata. Chitonida. 



