332 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



thick walls and a single large opening, just under the 

 letter v of Fig. 174. The embryo of Anodonta reaches 

 this stage of development within a few days after the eggs 

 are laid, and it remains almost without change until late 

 in the following spring. The parent then discharges the 

 larvae through the cloacal siphon into the water, where 

 they float for a short time. It is probable that all that 

 settle to the bottom die. Others are entangled by their 

 byssus threads to the tails, dorsal fins and gills of small 

 fishes. These close the valves of the shell onto the body 

 of the fish, driving the hooks into it. The setae probably 

 excite inflammation in the skin of the fish. At any rate the 

 epithelial cells of the skin grow at an unnatural rate, and 

 soon build up a covering over the larva, which is thus 

 enclosed in a brood-pouch, where it completes its develop- 

 ment, acquires gills, an oesophagus, stomach, intestine, 

 and renal organs and heart, and then escapes from the 

 brood-pouch and falls to the bottom to complete its 

 growth. 



XXIX.— THE GENERAL ANATOMY OF THE SQUID. 



(Loligo Pealii.) 



With a little thought the student should be able to 

 trace out the general anatomy of any Dibranchiate Cephal- 

 opod by the use of the following description, but as the 

 various forms differ greatly, he should, if possible, study 

 one of the squids. The description has been written from 

 Loligo Pealii, but any species of Loligo or Ommastrephes 

 will answer for laboratory work. 



Specimens may be obtained by the dredge or trawl, but 

 as they are frequently captured in great numbers by fish- 



