TABLE III. 



List of the most important differences in Animal Egg-cleavage and 



Gastralation.^^ 



The letters a-/ indicate the 6 animal tribes (the primitive animals being 

 excluded) : a, Plant-animals ; b, Worms ; c, Soft-bodied animals {Mollusta) ; 

 (i, Star-auimals {Echinoderma) ; e, Articulates {Arthropoda) ; f, Vertebrates. 



I. 



Total Cleavage. 



Segmffitatio totalis. 



Holoblastic Eggs. 



Gastrula with- 

 out 

 nutritive yelk. 

 Eblogastruku 



I- Original Cleavage. 



{Segmentatio primordialis.) 



Archiblastic eggs. 



Bell-gas 'rula. 



{Archigastrula.) 

 (Plate n. Fig. 1-6.) 



a. Most low Plant-animals (low 



Sponges, Hydrapolyps. Me- 

 dusae, Corals). 

 6. Many low Worms (Sigitta, 



Phoronis, Ascidia, many 



Nematodes, etc.). 

 A few low Soft-bodied animals 



(J/oMwsca)— Terebratula, .\r- 



giope, Pisidium. 

 Most Star - animals (EchinO' 



derma). 

 A few low Articulates (some 



Brancbiopods, Copepods, Tar- 



digrades). 

 /. The SlcuU-less Vertebrate (Am- 



phioxus). 



c. 



d 



e. 



n. Unequal Cleava'^e. 



{Segmentatio incequalis.) 

 Amphiblastic eggs. 



Hood-gastrula. 



(^Amphigastrula.') 



(Plate II. Fig. 7-17.) 



a. Numerous Plant-animals (many 



Sponges, Medusfe, Corals, 

 Siphon opliores, Ctenophoraj). 



b. Most Worms. 



c. Most Soft-bodied Animals {Mol- 



lusca). 



d. Individual Star-animals (vivi- 



parous species and a few 

 others). 



e. A few low Articulates (Ai-thro- 



poda) -hoth Crustaceans and 

 Tracheates. 

 /. Cyclostoma, Ganoids, Amphibia, 

 Mammals (all ?). 



n. 



Partial Cleavage. 



Scgmentatio partialis. 



Meroblastlc eggs. 



Gastrula with 



nutritive yelk. 



Meroyastrula. 





in. Discoidal Cleavage, 



{Segmentatio discoidalis.^ 



Discoblastic eggs. 



Disc-gastrula. 



{Disco-gastrula.) 



(Plate III. Fig. 18-24.) 



f 



c. Cuttle-fish, or Cephalopoda. 



e. Some Articulates (Arthropoda), 

 Millepedes, Scorpions, and 

 others. 



/. Primitive Fishes (Selachii), 

 Osseous Fishes, Reptiles, 

 Birds (and Monotremes r). 



IV. Superficial Cleavage. / 

 (^Segmentatio superficialis .) 

 Periblastic eggs. 



Bladder-gastru'a. 



(Perigastrula.) 

 (Plate III. Fig. 25-30.) 



a. A few Sponges (.?). 

 Alcyonium (/). 



6. Individual Worms (?) 



e. The great mnjority of Articu- 

 lates (Arth ropoda) — Crus- 

 taceans, Myriopods, Spiders, 

 Insects. 



