The chapter discusses the challenges faced by limnologists in North America and Europe in accessing each other's scientific literature. It highlights that 88% of the literature in PAUL S. WELCH's "Limnology" (1952) is in English, while 80% of FRANZ RUTTNER's "Grundriss der Limnologie" (1952) is in German. The author, ROBERT W. PENNAK, a student of Professor C. JUDAY, addresses this issue by introducing a valuable and well-organized treatise on freshwater invertebrates. The book, published by the Ronald Press Co. in 1953, is particularly useful for American biologists and zoologists but also for European readers due to its comprehensive coverage of various freshwater animal groups. Each chapter includes a general biological and morphological introduction, summarizing classical and recent investigations, including many important American papers. The book covers a wide range of topics such as general characteristics, morphological description, locomotion, feeding, internal anatomy, reproduction, seasonal variation, developmental life cycle, ecology, distribution, economic significance, and taxonomy. It concludes with a key to species or genera, accompanied by over 2,000 instructive figures. The author acknowledges the help of numerous specialists in refining the manuscript. The book is praised for its excellent text and attractive presentation, serving as a valuable resource for both North American and European limnologists.The chapter discusses the challenges faced by limnologists in North America and Europe in accessing each other's scientific literature. It highlights that 88% of the literature in PAUL S. WELCH's "Limnology" (1952) is in English, while 80% of FRANZ RUTTNER's "Grundriss der Limnologie" (1952) is in German. The author, ROBERT W. PENNAK, a student of Professor C. JUDAY, addresses this issue by introducing a valuable and well-organized treatise on freshwater invertebrates. The book, published by the Ronald Press Co. in 1953, is particularly useful for American biologists and zoologists but also for European readers due to its comprehensive coverage of various freshwater animal groups. Each chapter includes a general biological and morphological introduction, summarizing classical and recent investigations, including many important American papers. The book covers a wide range of topics such as general characteristics, morphological description, locomotion, feeding, internal anatomy, reproduction, seasonal variation, developmental life cycle, ecology, distribution, economic significance, and taxonomy. It concludes with a key to species or genera, accompanied by over 2,000 instructive figures. The author acknowledges the help of numerous specialists in refining the manuscript. The book is praised for its excellent text and attractive presentation, serving as a valuable resource for both North American and European limnologists.